* using `get_wch()` now and mapping most of the function keys documented
in `vterm_keycodes.h` (not num keypad)
* there are still a lot of mappings from ncurses missing (in conjunction
with modifier keys, related issue #11)
* using mutex to make sure writing to terminal client is serialized
* demo app: using `SHELL` environment var or `/bin/bash` as default
* removed some debug messages
* enabled all vterm screen handlers; if not implemented there is a debug
message
* fixed and improved cursor position — was sometimes off; e. g. if
pressing backspace
* stubs for some functions required for implementing #3
Christian Burger