Only set values if they're not nil
Allow ANKAPIResponseMeta to be resolved via ANKResourceMap
Add PaginatableResource class
Don't persist read-only properties
add support for parse_markdown_links
Interactions are paginatable
Expose unique "id" parameter/remove paginationID for some resources

I realize that in one of my previous patches I marked a few of these
as paginatable, when in fact they aren't.
Merge pull request #76 from berg/master

Upstreaming a bunch of stuff we use in the App.net app