Use ERR instead of 0 for modifier-less keybindings.

This allows C-space (NUL) as a normal key or modifier.
Scroll on Shift-PgUp and Shift-PgDn.
Completely redraw screen upon terminal size change
Source cleanups, no functional change
Add Mod-Tab to focus previously selected window
Reindent config.def.h
Cosmetic fixes for man page
Zoom to specific window

This is currently not hooked up from config.def.h
but can be used in the same way as focusn.
Hide cursor when scrolling
Hide window border if there exists only 1 client

This together with commit 756f9530 which hooks
scrolling up with Shift-Page{Up,Down} should make
dvtm a useful tool for st users who want a scrollback
buffer.
Remove screen lock functionality
Set version to 0.11
Update some year numbers
fix for v0.11