StepMania 5.0.9; release notes compiled and Markdown formatted by @kyzentun:

### This is divided into two sections:
* Player visible changes:  New configuration options players should try out,
* Themer visible changes:  New (optional) screens that themes can support, new metrics or lua functions, or fixes for existing functions.

Items are roughly grouped into the general part of StepMania they fit into.


# Compiling:
Cmake is now required for compiling Stepmania.  Read Build/README.md for instructions.  
The thread in the release forum has been updated with instructions for compiling on Linux.


# Player visible changes:

### BMS:
* .lua files defined in the #BMP tags now work as BG animations.  
* The #difficulty tag is now supported.  The difficulty numbers 1-6 map to
StepMania's difficulties from Novice to Edit.

### Bug fixes:
* Autokeysounds are no longer twice as loud when playing keysounded charts
with two players.
* 1 pixel seam in hold cap rendering fixed.
* Noteskin animation fixed.

### ScreenOverscanConfig:
There is a new screen for interactively adjusting the variables that already
existed in the preferences for dealing with overscan problems.  This allows
editing the CenterImage* preferences without restarting StepMania to set them
so that the whole image appears on screen.  
This currently handles the aspect ratio wrong, so it's not a perfect overscan
solution.


# Themer visible changes:

## Bug fixes and new functions:

* Attributes added are marked with [A].
* Bug fixes are marked with [B].
* Functions are marked with [F].

### Actor:
* [B] bounce and bob effects no longer round pixel coords.  
When an actor had a slow tween moving it in a direction and a slow bounce
effect, the bounce would round the resulting position and cause jitter.  That
jitter is gone now.
* [B] BlendMode_Subtract no longer crashes on the d3d renderer.  It does not
do proper subtraction blending, this is just a bandaid to prevent crashing.

### Global:
* [F] get_music_file_length
* [F] multiapproach function now takes an optional 4th argument to multiply
the speeds by.
* [F] update_centering

### OptionsList:
The OptionsListQuickChange, OptionsListLeft, and OptionsListRight messages
now have a Selection parameter that has the id of the selection the player
moved to.

### RageFile:
* [F] Flush

### ScreenInitialScreenIsInvalid:
If you see this screen come up, you need to fix the InitialScreen metric in
your theme.
