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