This adds very simple support for storing BMP files with
BITMAPV3INFOHEADER and BITMAPV4HEADER. This in turn allows us to
store alpha channels which is nice for our .pp file format. For
the moment no data regarding colorspace is saved, only the bare
minimum to make a valid file.
Some small restructuring of the code is made to hopefully make it
easier to implement more DIB-headers and support for colorspace/gamma
correction in the future.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
