Export AERC_MIME_TYPE and AERC_FILENAME in the filters command
environment. This allows dynamic coloring with tools that require
a filename and/or a mime type to determine the syntax.
Update docs and add example use in the default config file.
Signed-off-by: Robin Jarry <robin@jarry.cc>
Acked-by: Moritz Poldrack <moritz@poldrack.dev>
ebfd2a9da3