add support for the 68k calculators

[Ghost-Bit]

i own a ti 92 plus and would find it very useful to be able to use my chromebook to get files on it.

[debrouxl]

Adding support for a different cable + a different communication protocol + different file formats, and before that, refactoring to add the missing abstraction layers (which libti* has, for a reason)... while definitely useful and interesting, this is far from being a trivial endeavour :)