Sometimes the leader key gets in the way. Since my leader key
combination is C-a by default, this interferes with the (rare) times
that I want to increment something in vim (also C-a).
So, this commit allows toggling the leader key in wezterm off, so it
passes through to the actual applications. You can toggle it with
`C-Alt-a`.
Commit made possible with the help of the comments in this issue:
https://github.com/wez/wezterm/issues/656
Generalized the font used from special ligaturized Iosevka to the
standard Iosevka installed in the bootstrap process.
Changed from a blindingly bright default color scheme to a nice dark one
(Nord).
