Assuming no one uses C-b as the default prefix is a wrong assumption.
Instead of making any assumption about the prefix, we're "building" on
top of whatever the user has set.
The following key-bindings will be set if prefix is set to C-a:
- `C-a + C-a` - sends prefix character
- `C-a + a` - switches to the last window
Likewise, if C-b is prefix, then the additional bindings will be
`C-b + C-b` and `C-b + b`.
Closes#1
The `default-command` setting on OS X determines the default shell if
`default-shell` is not set.
This update enables use of any user defined shell, even if
`default-shell` is not set.
Fixes#2
