xinput: Cleanup implementation of XI up to v1.4

xinput: Cleanup implementation of XI up to v1.4

- Structural changes:
  * indent with spaces only (replaced tabs)
  * indent attributes
  * move structures in front of the first request using it
    (Otherwise c_client.py would generate uncompileable code if we fix
     the uninterpreted lists.)
  * add version-controlled section comments (types, requests, events,
    errors) and move structures into their corresponding section
  * sort events and eventcopys by number

- Additions:
  * add various missing enums and structs (i.e. DeviceChange,
    DeviceControl, DeviceName, ...)
  * uncomment commented out requests
  * linked in various enums into fields (via enum or altenum)

- Other changes:
  * link to the txt specification in the git repo
  * fixed comments for "uninterpreted lists"

- API CHANGES:
  * Request: GetDeviceMotionEvents
    The reply contains a list of events (of coordinates). So, we rename
    num_coords to num_events. The field is called nevents_return in the
    specification. The list was commented out anyways, so the rename
    shouldn't affect that much.
  * Request: SendExtensionEvent
    The list 'events' is a mask, make it a CARD8 like every other mask.
  * Events: FocusIn/Out
    Those ones haven't been named properly. They are called
    DeviceFocusIn/Out in the specification. In XI2 the names FocusIn/Out
    are used to introduce new events and cause name clashes. So, we have
    to rename the existing FocusIn/Out and give them their proper names.
  * Structures: *Feedback{Ctl,State}
    Rename the field id to feedback_id, as it's called in the spec. The
    only lists using those structs are commented out yet. So, this might
    not be called an api break.

Signed-off-by: Daniel Martin <consume.noise@gmail.com>