Add WKT parser.

Add a parser (read/write) for OGC Well-Known-Text (WKT). It deals with
geometries only, not with features, mostly because WKT can only contain a
single geometry (or geometry collection). This can later on be used to
serialize and deserialize geometries in ol3.
add exports for WKT
Don't rely on responseXML, also use responseText

On servers that report an incorrect content type for XML
documents, responseXML will be empty. In these cases we need to
use responseText instead. This change also prevents readNode
calls with empty data.
Use goog.isString() instad of typeof check
Merge pull request #713 from ahocevar/kml-responsetext

Do not rely on responseXML, also use responseText. r=@bartvde
address review comments by @twpayne
move last RegExp into constant
Merge pull request #712 from bartvde/wkt

Add WKT parser (r=@ahocevar,@twpayne,@tschaub)
GML options not always applied.

This is a follow-up for https://github.com/openlayers/ol3/pull/711
for the GML parser. Also use goog.array.map instead of map as was
pointed out by @twpayne on the WKT review and update the example data
to use all US states as pointed out by @tschaub on the Google hangout.
Merge pull request #714 from bartvde/gmloptions

GML options not always applied (=r@ahocevar)
Making RTree's find more efficient

By doing the type check before the intersection check, we can
save he intersection check for cases where we don't care about
type or have the specified type in a node.
Merge pull request #715 from ahocevar/rtree-performance

Making RTree's find more efficient. r=@bartvde