Better handling of mixing tabs and spaces; saner indentation when using C-j.
Make the mode usable under Emacs 23 (tested with 23.4).

Suggested by Steve Purcell, thanks!
Emacsen < 24 don't support lexical scoping. Remove it.
Highlight 'in' and 'or' as instructions rather than keywords.
Remove duplicate copyright line.
Fix erroneous higlighting of identifiers containing "macro" or "struc".
Use back-to-indentation instead of beginning-of-line-text to make indentation
behave correctly after comment lines.
(bobp) is a terrible bad of checking if we're at the first line. Since
forward-line doesn't signal an error, just remove the test.
Moving to github.