Update README and About menu command

+ Updated README to reflect recent changes
+ Changed 'About' menu command so that it uses the README.md instead of
a symlink to it placed under Support/
[theme] Update dummy theme
Update menu commands to reflect new scope naming scheme
Introduce global debug flag
[grammar] Rewrite language grammar

+ Stay close to the W3C parser spec
+ However, some rough edges are still there. Beside that the regular
expressions could partly be rewritten to achieve better performance (I
guess it'll notably sum up in the end)