* added wip implementation of orthographic rendering (mostly working, but needs separate render path -> need to compile and use additional kernels)
 * fixed sampling / fragment_coord (sample the pixel center instead of the pixel corner -> (x, y) + 0.5f)
 * added linear_blend macro, some math defines and made interpolate use "mad" instructions in oclr_math.h
 * added global minimal struct alignment define (OCLRASTER_STRUCT_ALIGNMENT) and added a oclraster_struct define (struct with such an alignment + packed) -> modified all code to use this
 * fixed dead lock on kernel reloading
 * added vector4 constructors for constructing a vector4 out of 2 vector2s, 1 vector2 + 2 floats and one single vector2 (.zw will default to 0 and 1 resp.)
 * reintroduced non-const get_default_framebuffer to pipeline (note that all modifications of the default framebuffer happen at your own risk)
 * fixed camera setup in combination with screen upscaling (-> removed the code, since this is no longer necessary/handled elsewhere)
 * some cleanup