Issue 10 ci add support for code spelling checks (#231)

* added make targets spell and codespell for spelling checks

* fix spelling errors detected by codespell

* added codespell to github workflow

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

src/bacnet/rp.c

@@ -91,7 +91,7 @@ int rp_encode_apdu(
 /** Decode the service request only
  *
  * @param apdu  Pointer to the buffer for encoding.
- * @param apdu_len  Count of valid bytes inthe buffer.
+ * @param apdu_len  Count of valid bytes in the buffer.
  * @param rpdata  Pointer to the property data to be encoded.
  *
  * @return Bytes decoded or zero on error.