Clarify what goes and what does not go into terminal.h

[certik]

A good rule seems to be:

• color output
• keyboard input
• querying terminal properties such as whether we are running in a terminal, terminal dimensions, etc.
• Screen class, that works like ncurses window
• Unicode support (input, output, Screen)
• Multiplatform support

Improvements, redesigns, etc. would go into terminal.h. It seems it's possible to keep it under, say, 2000 lines of code and have all this functionality in. So terminal.h would act as a multiplatform ncurses replacement.

Everything else (such as widgets) would go into other header files (or a separate library).

This scope of terminal.h should be documented in the README.

[staxfur]

@certik can we close this issue?

[certik]

Let's close this issue once it is documented in the README what the (new) structure is, what goes where and why.

[staxfur]

Sure! I'll add it to #147.