engine/terrain: removed redundancy for diagonal masks
engine/terrain: fix memory leak, reduce draw_mask array size
engine/terrain: storing texture id in draw_mask struct
engine/terrain: drawing the neighbor tile on top of the base

this equals the blending's final drawing step,
except that this tile will have to be blended first.
engine/shader: added this-> and using new[] instead of malloc
engine/texture: created basic structure for alphamasking
engine/terrain: drawing base texture with custom shader
engine/shader: added vertex attribute id fetching
engine/shaders: added seperate vertex shader for alphamasking
convert: setting alphamasks fully opaque again
engine/texture: restructured subtexture handling
engine/texture: started using vertex array objects for drawing
engine/shader: improved vertex attribute id querying
main: using seperate vertex shader for alphamasking
engine/shader: fixed missing error message and sign mismatch
engine/texture: more or less restored rendering
data/texture: enabled testing varying variables
engine/texture: reactivated texture drawing without shader
engine: moved camera to center of test map
engine/texture: sending position via vertex attribute now