Two new function:
BLF_shadow: set the level (for blur) and the shadow color.
BLF_shadow_offset: set the x and y offset for shadow.
(this is the current position plus offset)
By default shadow is not enable in the font, so before draw the
text you need call BLF_enable(BLF_SHADOW), also remember disable
the option in the end.
cb59bf722e