Engine: split out method for adjusting playing MP3 and OGG stream
Scripting: Fix segfault when compiling functions returning String[]

The variables inside a dynamic string array have a size of 0, causing
another lookup to take place on the return type. The compiler was
treating them as though they were references to forward-declared structs
types with a previously unknown size. This would be fine under normal
circumstances, but the STYPE_POINTER and STYPE_DYNARRAY flags were
causing the lookup to occur well outside the boundaries of the symbol
size array. Stripping these flags on the lookup allows this lookup
(albeit somewhat unnecessary) to find the correct size of the variables
in a string array.
ScriptAPI: implemented AudioChannel.Speed property

Additionally "AudioChannel::SetSpeed" function name is mapped to property setter for compatibility with Ahmet Kamil's (aka Gord10) custom engine.
Engine: split out a method for adjusting audio clip volume

This also fixes a bug that caused MP3 clip continuously increase its base volume if the directional modifier was applied
Merge pull request #203 from gurok/340_dynamic_array_fix

Scripting: Fix segfault when compiling functions returning String[]
Engine: another temporary fix for gfxfilter init from config

The configuration routine ought to be rewritten in a way that would let easier merging options from various sources (file, command line, etc).
Meanwhile, this fix should make custom filter scaling option work again.
Common: fixed missing members init in GUI ctors
Project: moved transparency unit conversions to Common lib
Common: use common transparency conversion for GUIMain
Engine: support for sprite blending modes
Common, Engine: GUI and sprite drawing routines use sprite blending