Improve FKCollectionsExtensions.

• Better header documentation snippets
• Better names for the block typedefs
• Add fk_parallelMap:
• Add fk_mapWithIndex:
• Add fk_indexOfFirst:
• Add fk_map: for NSDictionary
• Add fk_arrayWithoutObject:
• Add fk_arrayWithoutObjects:
• Add fk_mapSel:
• Add fk_filterSel:

This is basically a source dump from another
project, hence the monolithic commit. Sorry about
that.