~mcf/libblit

Build with -Wall -pedantic
vulkan: Remove some unused variables
Don't return void expression
Initial WIP amdgpu backend
Use a heredoc when generating config.mk
Slight reorginization of Makefile and configure
Add some initial manuals
Fix blt_image_get_userdata
BLT_FOURCC -> BLT_FMT
image: Destroy user data when image is destroyed
Allow attaching user data to images

This will be used to store associated X11 pixmaps and Wayland buffers.
Declare image and surface destroy functions
Move image functions to image.c
Move surface functions to surface.c
vulkan: Whitespace fix
vulkan: Check surface supported formats
Header dependencies
Initial vulkan backend
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