handle DCS status string requests
compat: add some csi dec private modes TODOs
compat: only clear cells when scrolling to add text

and to delete lines, but not when just moving the cursor
add termio_win_get();
compat: add ugly testing code to change between 80/132 cols
compat: add margin top support on Origin mode
compat: handle cursor-controls chars in ESC sequences
compat: csi parameters are always decimal

There can be some leading zeros.
compat: fix len computation when handling DCS escape codes
compat: improve doc/parsing on DCS escape codes
compat: discard (ftm) key resources used by xterm
compat: add some debug
compat: fix scrolling not clearing some text

Test case was provided by weechat.
compat: fix mouse wheel in utf8 mode

Closes task 87.
Tested with weechat.