#12 Update and Include .syn files

[Garrigues Benjamin]

Update xdfl.syn file for latest xdfl tags
(_module_compile, module_exec, script_exec, etc.).

Include .syn syntax highlighting files for textpad in
distribution, and/or as separate download.

Include or point to other usefull syn files (such as
xsl.syn).

Include readme.txt to show how to install .syn files in
TextPad.