Add FILE_LICENCE declarations to almost all files that make up the
various standard builds of gPXE.

curses.h so that you don't have to suffer the curses namespace pollution
just to get the symbolic key names.

abstraction.

- changes made to some constants and macros
- changes made to _curses_screen struct
- identified and removed prototypes for yet more unsupportable functions

- implemented hline/vline (part of wborder family)
- screen cursor now relocates at same time as window cursor when
  restoring after a non-wrapping function

- fixes to wborder (same)
- addition of a few minor functions

- added extern declarations for global vars
- removed comments from static inlines (too time consuming to do them
  all, considering all so far have been due to the ridiculous amount of
  redundancy within the API spec)
- removed a few more extern func decls for funcs that cannot be
  implemented at this time