* Player character now experiences acceleration and friction when
walking around the map!
* Actor position and movement had to be converted from int's
(render.Point) to float64's to support fine-grained acceleration
steps.
* Added "physics" package and physics.Vector to be a float64 counterpart
for render.Point. Vector is used for uix.Actor.Position() for the sake
of movement math. Vector is flattened back to a render.Point for
collision purposes, since the levels and hitboxes are pixel-bound.
* Refactor the uix.Actor to no longer extend the doodads.Drawing (so it
can have a Position that's a Vector instead of a Point). This broke
some code that expected `.Doodad` to directly reference the
Drawing.Doodad: now you had to refer to it as `a.Drawing.Doodad` which
was ugly. Added convenience method .Doodad() for a shortcut.
* Moved functions like GetBoundingRect() from doodads package to
collision, where it uses its own slimmer Actor interface for just the
relevant methods it needs.
Add new doodads:
* Start Flag: place this in a level to set the spawn point of the player
character. If no flag is found, the player spawns at 0,0 in the top
corner of the map. Only use one Start Flag per level, otherwise the
player will randomly spawn at one of them.
* Crumbly Floor: a solid floor that begins to shake and then fall apart
after a moment when a mobile character steps on it. The floor respawns
after 5 seconds.
* State Blocks: blue and orange blocks that toggle between solid and
pass-thru whenever a State Button is activated.
* State Button: a solid "ON/OFF" block that toggles State Blocks back
and forth when touched. Only activates if touched on the side or bottom;
acts as a solid floor when walked on from the top.
New features for doodad scripts:
* Actor scripts: call SetMobile(true) to mark an actor as a mobile mob
(i.e. player character or enemy). Other doodads can check if the actor
colliding with them IsMobile so they don't activate if placed too close
to other (non-mobile) doodads in a level. The Blue and Red Azulians
are the only mobile characters so far.
* Message.Broadcast allows sending a pub/sub message out to ALL doodads
in the level, instead of only to linked doodads as Message.Publish does.
This is used for the State Blocks to globally communicate on/off status
without needing to link them all together manually.
* Implement the handler code for `return false` when actors are
colliding with each other and wish to act like solid walls.
* The locked doors will `return false` when they're closed and the
colliding actor does not have the matching key.
* Add arbitrary key/value storage to Actors. The colored keys will set
an actor value "key:%TITLE%" on the one who touched the key before
destroying itself. The colored doors check that key when touched to
decide whether to open.
* The trapdoor now only opens if you're touching it from the top (your
overlap box Y value is 0), but if you touch it from below and the door
is closed, it acts like a solid object.
