Move memdraw functions to appropriate header.
Let _al_clear_memory take target bitmap as an argument.

No need to abuse TLS here.
Move bitmap memory/video type conversion to separate file.
Rename awkward symbols related to the bitmap conversion list.
Remove _al prefix on static functions.
Move _al_transform_is_translation declaration to appropriate file.
Move _al_blend_memory declaration to appropriate file.
Move _al_draw_bitmap_region_memory declaration to new file.
Move _al_put_pixel out of public header.

This change should removes a function which was inadvertently exported,
so should probably NOT be backported to the 5.0 branch.
Do not publicly export _al_put_pixel on the 5.1 branch.

It probably won't break binary compatibility, except for people who
shouldn't be calling it in the first place, but, to be safe, don't
backport this to the 5.0 branch.
Delete unused ALLEGRO_MEMORY_BLENDER type.
Move exit functions to separate file.
Move logging and assertion handlers to new file.
Delete unused definitions of al_(un)register_system_driver.
Move _AL_DRIVER_INFO into an internal header.
Remove al_create_custom_bitmap.

It would be unusable without intimate knowledge of Allegro.
Delete al_ortho_transform compatibility macro.
Seed _al_rand when the system driver is installed.
docs: Mention how al_make_temp_file generates the file name.
video: Replace deprecated av_find_stream_info() call.