When storing the sassified css, also store copies compressed with gzip
and brotli. That way, a good web server and client can save some
bytes of file transfer (the css in this project is very small, but as
it grows, this will become more relevant).
This currently uses the sass-sys low-level interface, because the
operation is not supported in sass-rs.
The PR https://github.com/compass-rs/sass-rs/pull/3 adds high-level
support. If / when that is fixed, the direct requirement for sass-sys
should be removed from rphotos.
The css file is built to a file with (short) checksum in the
file name, to be nicely cacheable. The actual file name is
compiled into the binary and sent to the templates as a variable.
