Areas and places

Should resolve #119 as well as adding places; this should also update other bits of the WS that return places and areas (e.g. in relations, but also intrinsic properties such as begin/end area). I've also updated other sections of the code -- valid search includes (via the Indexed Search Syntax wiki page), valid release types (via some database queries), and a few format fixes:

* URL MBIDs are available via the 'id' attribute of the 'target' element in relations. Where present, this is now the 'target-id' key; where it's not (i.e., other elements), the text of the target element is put into the 'target-id' key, such that 'target-id' is now a place where users can reliably get an MBID (versus 'target', which will have a URL in the case of URLs, and an MBID otherwise).
* Link type UUIDs are now available via the type-id key, parsed from the type-id attribute of the link.

One thing I've not done though it does concern areas indirectly is update the code to deal with multiple release events. However, having a parse_area will also expediate that process.