Replace internal bookmarks list with a dictionary, part 1
Replace internal bookmarks list with a dictionary, part 2
Reduce amount of useless bookmarks dict copying
Simplify bookmarks navigation
Replace OrderedDict for bookmarks with regular one

Appears to be useless in the end.
Speed up handling of large scripts with enabled automatic calltips
Speed up slider redrawing with many bookmarks

Since we don't do any subpixel drawing we can skip drawing bookmarks of
the same type with the same start pixel position. This will greatly
improve performance of any operations that cause slider redrawing (e.g.
navigation) when many bookmarks are placed near each other.
Merge pull request #16 from tp7ptr/master

Bookmarks handling improvements/optimization