Restore the WKT parser, example & tests

This is a first attempt to restore the WKT parser.
It is probably preferred to rewrite the parser to the `ol.format` namespace as well,
but I would first like to have some confirmation on this before doing so.
For this to be documented (and so the compiler doesn't rename properties), you have to add `olx.format.WKTOptions.prototype.splitCollection` and a corresponding doc block.  See [`olx.format.KMLOptions`](https://github.com/gingerik/ol3/blob/restore-wkt-parser/externs/olx.js#L1160-L1171) for inspiration.