[RFC] Extract line_consumption.c from misc1.c

This pull request extracts some functions that are concerned with physical line consumption of a buffer on screen from `misc1.c` and puts it in a file called `line_consumption.c`. (See #209)
Completely correct, I'm afraid. Pure functions can change no global state, and I believe the allocated memory is global state, among others.

Perhaps there is a way to rewrite the function without allocating.