now disposing objects when they are overwritten by new ones in AssetManager (closes #467)

Furthermore, added dispose/clear calls for XMLs and ByteArrays in 'dispose' method.
added missing support for Vectors in "profile" argument; now picking lowest available profile in older AIR versions (instead of the first list element) (refs #337)
added more api docs about render context and context loss (refs #337)
now surviving a context loss happening while processing the asset queue (closes #472)
added missing 'handleLostContext' check
now enforcing passing of single profile to Starling constructor in shared context scenarios
added 'transformationMatrix' property to 'SubTexture' class (closes #470)
changed automatic profile selection to prefer known profiles in fallback solution (refs #337)
fixed position of clear call in main render method (closes #468)
avoiding side effect of profile selection (refs #337)
partly fixed support for restoring cached filters on a context loss (refs #474)

Only works for textures that can be synchronously updated, though.
Merge branch 'master' into develop