New configuration API

[joshgoebel]

• document
• "how to" upgrade from xkeysnail to keyszer
• keymap 6f3e1a5
• cond_keymap 6f3e1a5
• modmap cae3135
• cond_modmap cae3135
• multipurpose_modmap e219e45
• conditional_multipurpose_modmap e219e45

[joshgoebel]

Need some match helpers now to avoid ugliness like this:

    conditional(lambda ctx: re.compile("Firefox").search(ctx.wm_class),
        keymap("Firefox",{
            K("C-M-j"): K("C-TAB"),
            K("C-M-k"): K("C-Shift-TAB"),
        })
    )

Since now the requirement is we always pass a function, we may need a few helpers to tidy this up.

IE:

conditional( wm_class_matches_regex("Firefox"), # ...

Or something... We can't just pass raw regex around anymore because the target isn't clear... device name? wm class? wm name (soon)? other?