Feature/raspberry pi blinkt color objects (#503)

* fixed BACnetXYcolor and BACnetColorCommand encode and decoding and improved unit test coverage. Refactored BACnetXYcolor to/from ascii into lighting module.

* added to the color, color temperature, and lighting output objects a fade/ramp/step engine.  Added color and color command coercion into the channel object and enabled color temperature object coercion.  Added CreateObject and DeleteObject service handling to the color, color temperature, lighting output, and channel objects.

* added blinkt demo app for Raspberry Pi [WIP]

* updated gitignore to simplify handling of apps folder contents

* fixed piface demo build

* added RaspiOS to pipeline for piface and blinkt! demo builds

* added device object timer function for child object types into example Device object.  Refactored device object to increment database revision for create or delete object services.   Refactored example app/server to use mstimer library and device child object timers.

---------

Co-authored-by: Steve Karg <skarg@users.sourceforge.net>

src/bacnet/basic/sys/linear.c

@@ -0,0 +1,128 @@
+/**
+* @file
+* @author Steve Karg
+* @date 2011
+* @brief Performs linear interpolation using single precision floating
+* point math or integer math, or a mixture of both.
+*
+* @section LICENSE
+*
+* Copyright (C) 2011 Steve Karg <skarg@users.sourceforge.net>
+*
+* Permission is hereby granted, free of charge, to any person obtaining
+* a copy of this software and associated documentation files (the
+* "Software"), to deal in the Software without restriction, including
+* without limitation the rights to use, copy, modify, merge, publish,
+* distribute, sublicense, and/or sell copies of the Software, and to
+* permit persons to whom the Software is furnished to do so, subject to
+* the following conditions:
+*
+* The above copyright notice and this permission notice shall be included
+* in all copies or substantial portions of the Software.
+*
+* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+*
+* @section DESCRIPTION
+*
+* Performs linear interpolation using single precision floating
+* point math or integer math, or a mixture of both.
+* Linear interpolation is a method of constructing new data
+* points within the range of a discrete set of known data points.
+*/
+#include <stdbool.h>
+#include <stdint.h>
+#include "linear.h"
+
+/**
+* Linearly Interpolate the values between y1 and y3 based on x.
+*
+* @param  x1 - first x value, where x1 <= x2 <= x3 or x1 >= x2 >= x3
+* @param  x2 - intermediate x value, where x1 <= x2 <= x3 or x1 >= x2 >= x3
+* @param  x3 - last x value, where x1 <= x2 <= x3 or x1 >= x2 >= x3
+* @param  y1 - first y value, where y1 <= y2 <= y3 or y1 >= y2 >= y3
+* @param  y3 - last y value, where y1 <= y2 <= y3 or y1 >= y2 >= y3
+* @return y2 - an intermediate y value y1 <= y2 <= y3 or y1 >= y2 >= y3
+*         and the y value is linearly proportional to x1, x2, and x2.
+*/
+float linear_interpolate(float x1,
+    float x2,
+    float x3,
+    float y1,
+    float y3)
+{
+    float y2;
+
+    if (y3 > y1) {
+        y2 = y1 + (((x2 - x1) * (y3 - y1)) / (x3 - x1));
+    } else {
+        y2 = y1 - (((x2 - x1) * (y1 - y3)) / (x3 - x1));
+    }
+
+    return y2;
+}
+
+/**
+* Linearly Interpolate the values between y1 and y3 based on x
+* and round up the result.  Useful for integer interpolation.
+*
+* @param  x1 - first x value, where x1 <= x2 <= x3 or x1 >= x2 >= x3
+* @param  x2 - intermediate x value, where x1 <= x2 <= x3 or x1 >= x2 >= x3
+* @param  x3 - last x value, where x1 <= x2 <= x3 or x1 >= x2 >= x3
+* @param  y1 - first y value, where y1 <= y2 <= y3 or y1 >= y2 >= y3
+* @param  y3 - last y value, where y1 <= y2 <= y3 or y1 >= y2 >= y3
+* @return y2 - an intermediate y value y1 <= y2 <= y3 or y1 >= y2 >= y3
+*         and the y value is linearly proportional to x1, x2, and x2.
+*/
+float linear_interpolate_round(float x1,
+    float x2,
+    float x3,
+    float y1,
+    float y3)
+{
+    float y2;
+
+    y2 = linear_interpolate(x1, x2, x3, y1, y3);
+    /* round away from zero */
+    if (y2 > 0.0) {
+        y2 += 0.5;
+    } else if (y2 < 0.0) {
+        y2 -= 0.5;
+    }
+
+    return y2;
+}
+
+/**
+* Linearly Interpolate the values between y1 and y3 based on x
+* using integer math.
+*
+* @param  x1 - first x value, where x1 <= x2 <= x3 or x1 >= x2 >= x3
+* @param  x2 - intermediate x value, where x1 <= x2 <= x3 or x1 >= x2 >= x3
+* @param  x3 - last x value, where x1 <= x2 <= x3 or x1 >= x2 >= x3
+* @param  y1 - first y value, where y1 <= y2 <= y3 or y1 >= y2 >= y3
+* @param  y3 - last y value, where y1 <= y2 <= y3 or y1 >= y2 >= y3
+* @return y2 - an intermediate y value y1 <= y2 <= y3 or y1 >= y2 >= y3
+*         and the y value is linearly proportional to x1, x2, and x2.
+*/
+long linear_interpolate_int(long x1,
+    long x2,
+    long x3,
+    long y1,
+    long y3)
+{
+    long y2;
+
+    if (y3 > y1) {
+        y2 = y1 + (((x2 - x1) * (y3 - y1)) / (x3 - x1));
+    } else {
+        y2 = y1 - (((x2 - x1) * (y1 - y3)) / (x3 - x1));
+    }
+
+    return y2;
+}