Add libmagic to better process mime_types on Linux

[masmullin2000]

Problem: serving files as application/application-octext-stream is annoying if the file is ASCII text

Solution: When serving files on linux, libmagic can analyze the file to determine filetype when mime_guess has failed. Use libmagic to determine if a file is a plaintext file.

Signed-off-by: Michael Mullin [email protected]

[TheWaWaR]

Please fix CI