Revert "Externalise itags"

This reverts commit 6dd79ea90f0207ff392300890e3b318bcc446b08.

Conflicts:
	configs/itags
	yturl
Remove external itags info from setup and manual
Drop manual support, change to markdown readme
Drop distutils
New itags: 36, 46
Add information on usage to readme
Invocation instructions for shell function
Major restructure of YTURL.

- All in one class
- Allow usage of -q/--quality
Make help messages consistent with --help default
Correct documentation

- -q high is implicit
- Not the first one we find, but the closest to the lowest itag
Add -q medium, default to it
Clarify that we can't always get the exact itag wanted
itag is %s, not %d.
Exit after reporting no itags
Add InvalidItagError
Fix __doc__ for InvalidItagError
Match --help output to readme
python -> python2 in shebang