I guess it never got written because no one has asked about it yet (until now) and most people have had no issue porting i2c libraries - generally it's pretty straightforward -
This has worked for all the libraries I've ported:
include tinywirem.h
in setup call TinyWireM.begin()
comment out Wire.h
replace all Wire.write/send with TinyWireM.send
same for read/receive
That's it - if that doesn't work let me know and I'll take a look at the library as soon as I have a chance