Add TODO list
Implement chord chains

And also:
- Allow commands and hotkeys to be spread across multiple lines.
- Allow sequences to be present in the hotkey and not in the command and
  vice versa.
- Handle literal braces and commas via the backslash inhibitor.
Fix small typo
Compact debug notation for bindings
Don't clobber system build flags
Preserve mode via cp's `-p` option
Keep order of configuration in hotkeys
Reorganize code
Handle *nested* sequences
Integrate the keysym into the modfield

In order to make the following work:

    @Control_L
        echo hello

we must subtract the modfield of the keysym from the modifier state of
key release event. The reason being that the modifier state we receive
is generated before the key release. It means that releasing `Control_L`
will generate a key release event whose state will most probably contain
the bit mask of the control modifier.
When there's no waiters, abort the chain
Handle empty sequence elements via '_'
Enforce clean sequence expansion
The `hits` variable is redundant
Generate documentation via `pandoc`
Only use bold and italic whenever possible
Don't nest bold and italic
Reprocess a chord when it breaks a chain
Generate documentation via `asciidoc`
Prevent brace interpretation