Feature/comments and review (#102)

* Added comments. Replaced -1 with BACNET_STATUS_ERROR macro.

* Added some DogyGen comments

* Added missing return value check for booleans.

* Check used bits against unused bits in bitstrings.

* Added missing return value check for bitstrings.

* Added sanity checks and comments.

* Fixed implicit type conv warning.

* Chose to keep simpler C function methods.

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

src/bacnet/event.c

@@ -507,7 +507,7 @@ int event_notify_decode_service_request(
                 /* tag 9 - ackRequired */
                 section_length =
                     decode_context_boolean2(&apdu[len], 9, &data->ackRequired);
-                if (section_length == -1) {
+                if (section_length == BACNET_STATUS_ERROR) {
                     return -1;
                 }
                 len += section_length;