The terminal is assumed to be 80x24 in size, the new options
`term_width_limit` and `term_height_limit` can be used to overwrite
that.
Lines longer then the terminal width cause problems with scrolling
pages and need to be shortened.
The algorithm used for shortening can deal with tabs and escape
sequences, has rudimentary support for UTF-8 and runs in O(n).
avih helped in the creation of the term_ellipsis() function and split()
is also from him.
Christoph Heinrich
777f69bee8