The adapted upng has a very compact fully-stateful lws-aligned
implementation already.
Adapt it to also be buildable and operable standalone, and to
understand gzip headers.
Provide some apis to inflate gzip simply reusing opaque inflator
contexts from upng.
Provide an api test that inflates gzip files from stdin -> stdout
Add a rewritten version of upng that decodes statefully line by line, and so
does not require a bitmap buffer for the output. This compares to original
upng approach that needs heap allocations for the input, the whole output
and intermediate allocations.
Instead of buffers for input, decompression and output, it only allocates
2 x lines of RGBA pixels (ie, a few KB), and 32KB of decompressed data for
backward references in the decoder, and decodes as needed into the 2-line
buffer to produce line rasterized results. For a 600px width PNG, this is
just 40KB heap for the duration.
