Add debugging output in key map creation

Requires the addition of a debug flag to `parse_mapping` and `parse_token`.

For some reason there is no declaration of the function `parse_token`. I'm
not sure why so I won't add it.
Change to using KeySyms rather than keycodes to store to-keys

Modify all code to store and manipulate KeySyms instead of KeyCodes for
output key data.

Incomplete in two places (both also noted by comments in the code):

* When creating the additional key press events I have not yet implemented
  the switch to using `XSendEvent` rather than `XTestFakeKeyEvent`. Instead
  I just convert back to a keycode assuming zero shift level and
  group. This gives the same behaviour as before.

* When checking that an event is not one that we generated I haven't managed
  to figure out how to get the keysym of the event from the data provided
  by X. Instead I compare the key codes for now, which will work until the
  above issue is fixed.
Convert numbered lists in readme to proper markdown lists
Modify readme to explain how to generate button presses with shift
Revert "Change to using KeySyms rather than keycodes to store to-keys"

This reverts commit b1f0a0601b10fdc76e19d858fe10c820561b6a09.
Add example: make space generate ctrl if held
Merge pull request #22 from davidshepherd7/master

Additions to readme and debugging output during keymap creation