Custom checksums, multi-part frames

This release adds support for custom checksums, the 1-wire type XOR8 and for sending multi-part frames.

Multi-part frames can have their payload generated on-the-fly without having it all available at once to be passed to the send functions. Those are the *_Multipart send functions.

See the updated README.MD for details.

MIGRATION

Some changes are needed to update to this version:

• Added config key: #define TF_USE_MUTEX 1
  • set to 1 if you provide external implementation of the mutex functions.
• All occurences of size_t were replaced with uint32_t. This includes TF_WriteImpl(). Update your TF_WriteImpl() to use uint32_t for the last argument.
• TF_ClaimTx() now returns false if the mutex could not be claimed. This results in the Send functions returning false and a message being printed using TF_Error(), if provided