BoostSet: Add 'remove' and rename BoostHash::erase to remove

This is more consistent with Qt's method naming.
Core/MRI: Fix handling of Etc/Font properties

The gist of it is that for Etc and Font props, the assignment
operator (eg. 'sprite.color=') does not take a reference of the
right hand parameter and replaces its previous one with it (this
was the old behavior). Rather, it keeps its internal property
object and copies the parameter object into it by value.
The getter is unchanged; it still returns a reference to the
internal property object.

s = Sprite.new
c = Color.new
s.color = c
p s.color == c # => true
p s.color.object_id == c.object_id # => false (true before)
c = s.color
p s.color.object_id == c.object_id # => true
Bindings: Remove 'wrapNilProperty'

It's completely useless lol.
Small compilation fix (mruby is still broken though)
Config: Correctly setup rgssVer / screen size with customScript
MRuby: Fix handling of Etc/Font properties

Port of f8c26fc515cb4fb6b24b766889d4b0b0a3c12a26.
MRI: WindowVX dummy contents object is always created

The check was against rgssVer >= 2, but since that's always
true if WindowVX is used, it was pointless.
Core, MRI: Don't expose RGSS3 functionality in 2
TilemapVX: Use SimpleShader for unanimated ground layers

Also remove some useless member variables.
Bitmap: Don't use 'pixman_region_clear'

It's not included in older pixman versions.
Load fluidsynth entrypoints dynamically (and make them optional)

This removes the static dependency on fluidsynth being present
at buildtime (even headers aren't needed anymore).

Even though midi is a default format for the RPG XP/VX series,
it has fallen more and more out of use, with VX Ace completely
abandoning it from the RTP and making ogg vorbis the de facto
standard. Midi support is kept for legacy reasons, but isn't
encouraged. On top of all this, fluidsynth together with glib
is a heavy dependency that often times won't even be used.
Making it optional at build time is an attempt to unify and
keep build config fragmentation low.

In RGSS3, fluidsynth / midi is not initialized at all by
default, but rather on demand when either a midi track is
played back or Audio.setup_midi is called.
SDL_sound: Add wave IMA ADPCM (4bit) support patch
Spacing
check Ruby strings for embedded null bytes

The RGSS doesn't do it. But doing it shouldn't be a problem, as it's the
correct way. If a game is broken by this commit (unlikely), then the game
needs to be fixed as silent truncation is highly unlikely to be wanted.
VX tilemap has 9 bitmaps
Merge pull request #68 from cremno/vxtilemap-has-9-bitmaps

VX tilemap has 9 bitmaps
Merge pull request #69 from cremno/check-ruby-string-for-embedded-null-bytes

MRI: check Ruby strings for embedded null bytes
Couple fixes to last SDL_sound patch
MRI: load_data: Catch exceptions and pass onto ruby
README: Remove erroneous line about cmake