Add camel_mime_parser_init_with_input_stream().

Similar to camel_mime_parser_init_with_stream(), but takes a
GInputStream instead of a CamelStream.
Reimplement camel_mime_parser_init_with_fd().

Now creates a GUnixInputStream and hands it off to
camel_mime_parser_init_with_input_stream().

Removed functions:

  camel_mime_parser_fd()