Guy: rename dash to grounddash

so that in the future we can add a new dash type: airdash. They are
treated as completely different and unrelated abilities, EXCEPT for the
fact that they're both triggered by the same input.  The input logic
will be responsible for determining which ability to execute based on
the player state (`is_on_ground`)
Guy: add airdash properties and empty APIs
Rename dash_powerup.js -> grounddash_powerup.js
Rename DashPowerup -> GrounddashPowerup

also fix incorrect reference to Guy.can_dash
Add Guy._handle_yes_collisions()

and do the on_ground stuff properly
Remove a bunch of potentially confusing comments

I STILL don't have the whole state machine & separation of concerns
thing figured out, so I don't want to set anything in stone yet. But
this means that I will have to be very very careful when
adding/changing states in the future. VERY careful. But at least I won't
have misled myself (hah!)
Add airdashing functionality

weeeee big commit sorry
Merge branch 'topic/ghi/16' into dev

Fixes Github issue #16
Add powerup for airdash
Merge branch 'topic/ghi/41' into dev

Fixes Github issue #41
Consolidated mouse_display and fps_counter

Also added a display for player pos
Merge branch 'topic/ghi/40' into dev

Fixes Github issue #40
Rename powerup.js to onion.js

To get ready for the future!
Rename Powerup to Onion
Move physical -> 0-physical

My stupid game.cgi script sorts alphabetically. That's terrible
Remove lib from gitignore

Why was that even there?
Add consolidate script

Copied from my code/lang directory, and modified such that it can be
imported as a module, rather than running as a script
Huuuuuuuuge reorg, sorry

I actually implement consolidate in game.cgi, so everything needs to be
moved around. I also did a bunch of house cleaning - removing stuff that
either I no longer need, never needed in the first place, or will not
need until waayyy in the future
Reorganize object hierarchy - almost

Still missing terrain
Merge branch 'topic/ghi/39' into dev

Fixes Github issue #39