Re-add the use_cache at setstate.

This makes it possible to load a screen that uses use.
Speed up style selection.

We do this by cheating heavily - avoiding re-preparing screens, and
busting the render cache. This wouldn't work for arbitrary code,
but it's good enough for the theme chooser.
Share code between the RollForward action and behavior.

This makes the action work properly.

Fixes #436.
tts: Allow the alt property of Text to take [text].

This makes it possible to wrap the text with prefixes and suffixes
on a per-Character basis, so as to more accurately convey meaning.
tts: Strip " before passing text to windows.

Windows command line argument parsing strikes again. This seems to
let text pass through in a way that makes it reasonably correct.
tts: Document what_alt.
Optionally, automatically build_all on distribute if pyx changed.
Check in profile_screen.
Set all-state Transform properties on initialization.

This lets users of a Transform access its properties before it
has been rendered or updated for the first time.
Ensure hiding is always an attribute of screens.

Fixes compatibility with 6.17.

See: Lovely Little Thieves 0.5
Ensure hiding is set on legacy ScreenDisplayables.
placeholder: Add Placeholder displayable.

This displays a placeholder image. The image displayed may be chosen
by the creator, or automatically determined based on the name of the
image being placeheld.
Use Placeholders for missing images.
Update editor.rpy

translated some lines
atl: Properly compute const-ness for a function statement.

Fixes #449.
Reorder methods in Script.
script: Commit to loading a file when it parses/unpickles.

This prevents an error that was caused by when an exception in
finish_load would cause the .rpy file to load after finish_load
had already started updating data structures.
ATL transforms now begin executing when first shown.

Previously, ATL transforms began executing when the screen containing
the ATL transform was first shown, which meant that if the transform
changed over the course of screen display, a portion of the new
transform would be skipped.
Properly document the third argument to edgescrill.

Fixes #447.
Document Placeholder.