filenameToUri
Converts an absolute filename to an escaped ASCII-encoded URI, with the path component following Section 3.3. of RFC 2396.
Return
a newly-allocated string holding the resulting URI, or null on an error.
Parameters
filename
an absolute filename specified in the GLib file name encoding, which is the on-disk file name bytes on Unix, and UTF-8 on Windows
hostname
A UTF-8 encoded hostname, or null for none.