fix warning: use size_t when comparing against strlen()
default config: use `set` for directions

Using `set` for direction letter keys makes them easier to configure for
users who prefer traditional vim-style directions.
also change the default font in i3.config.keycodes
Bugfix: don’t overwrite the original size of floating windows when changing border style

fixes #1263
Bugfix: don’t errnously render floating fullscreen windows during restart

fixes #1263
Bugfix: ensure floating windows don’t drop out of fullscreen when restarting

fixes #1263
Bugfix: don’t overwrite the window’s geometry after restarting

fixes #1263