Bugfixes, Function offset H codes, Extension ABI improvements

/H codes can now be offset from functions like AGTH.

Bugfixes:
Extensions with underscores in their name don't screw everything up.
Extensions can use different CRT libraries.
Fixed crash when too many text threads are added.
Error message improved.

THIS UPDATE BREAKS OLD EXTENSIONS UNLESS YOU REBUILD THEM WITH UPDATED CODE

Beta release: may break easily.
You might have to install the Microsoft Visual C++ Redistributable before running Textractor.