Added static files processing and mime types using libmagic. Libmagic is the unix
library for infering mime types from files (used in the file command).

conf.h : added magic field in conf_t needed to store libmagic state
master.c : added libmagic initialization
dispatcher.c : give filename instead of uri to serve_static
serve_static : mmap the file and send the response
mime.c / mime.h : gives the mime type for a given filename using libmagic