libxo-0.5.0

• document "trim" modifier
• add xo_emit_field functions
• Add xo_set_file{,_h} functions
• Fix LIBXO_* variables; add -L and -I as needed
• add --disable-silent-rules and an explicit make; s/PACKAGE-NAME/PACKAGE_NAME/; add /download/ to 'url'
• fix silliness where xo_flush_h emitted closing tag (html); make the caller (xo_message) do it
• flush after transitions; fix flush call in xo_do_emit
• mkdir the version-specific packaging dir
• use "XO__" instead of LIBXO__