Implement GPX parser (read/write).

Implement a parser for GPX which supports read and write.
Small fixes for KML write.

Be a good XML citizen and always write out schemaLocation.
Use serialize on ol.parser.XML so that we don't have to set xmlns manually.
address review by @fredj
make feature info work on touch devices for gpx example see #727
Fixing bug in tests

That's what you get from copying and pasting and forgetting to
modify the pasted lines to suit your needs.
Merge pull request #730 from ahocevar/fix-rtree-tests

Fixing bug in tests
RTree API improvements and more tests

This change reverts the RTree API back to the original one (i.e.
insert() instead of put(), search() instead of find()), and
creates a new searchReturningObject() method that returns an
object keyed by UIDs.

It also adds missing tests for type restricted search and
searchReturningObject().
Write support for ol.parser.GeoJSON

Also add some convenience with static read and write methods based on the
singleton.
Merge pull request #726 from bartvde/kml_serialize

Small fixes for KML write (r=@ahocevar)
Merge pull request #731 from ahocevar/rtree-api-tests

RTree API improvements and more tests. r=@twpayne
Store the feature's commonly used id

To not clobber the feature's attributes, this is a separate
member property.
Store the KML Placemark identifier
Merge pull request #732 from bartvde/geojson-write

Write support for ol.parser.GeoJSON (r=@tschaub)
Fix XML serialize and xml_eql in IE9

Use the xml property instead in IE for serializing XML.
The xml_eql tests were failing in IE9 on a difference between null and an
empty string for namespaceURI of attributes, this difference is not
relevant to our testing so make sure we ignore.
fix typo in WMTS parser
Merge pull request #2 from fredj/fid

Store the KML Placemark identifier
Merge pull request #733 from ahocevar/fid

Store the feature's commonly used id. r=@fredj,@bartvde
Add parser.jsdoc file for docs on parser options.

Pointer by @ahocevar in #735
Merge pull request #736 from bartvde/jsdoc2

Add parser.jsdoc file for docs on parser options (p=@ahocevar, r=@bartvde)
FeatureId support in GML (r/w) and KML (w)

Now that we have FeatureId support (see #733), we can add this back to the
GML parsers (v2 and v3). Also add write support for FeatureId in KML, read
support was already added by @fredj