v0.2.1

Updated to support compilation and use with SDCC 4.2.0, which has changed to a new ABI for STM8. The changes force use of the previous ABI calling convention for all library functions. There are no changes to library functionality. Also note that this change will not require the use of the old calling convention on any of your code that utilises this library.

Please be warned that at some point in the future all the assembly code in the library will be updated to use the new calling convention, and at that point will no longer be usable with code compiled with SDCC versions older than 4.2.0. When that change will happen is yet to be decided.