Updated bootloaders to use the new main() function layout and remove any references to the scheduler to keep them in line with the rest of the library.

Fixed incorrect ENDPOINT_EPNUM_MASK mask preventing endpoints above EP3 from being selected (thanks to Jonathan Oakley).

Removed STREAM_CALLBACK() macro - callbacks now use regular function definitions to clarify user code.

Removed DESCRIPTOR_COMPARATOR() macro - comparators should now use regular function definitions to clarify user code.

Corrections to Keyboard demo.

Removed AVRISP_Programmer project due to code quality concerns.