Implement GPX parser (read/write).

Implement a parser for GPX which supports read and write.
address review by @fredj
make feature info work on touch devices for gpx example see #727
Write support for ol.parser.GeoJSON

Also add some convenience with static read and write methods based on the
singleton.
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
Sort exported properties
Export constrainResolution and constrainRotation from ol.View2D
Merge pull request #741 from fredj/export-view-constraints

Export constrainResolution and constrainRotation from ol.View2D
Merge pull request #737 from bartvde/feature-id

FeatureId support in GML (r/w) and KML (w) (r=@fredj)
Merge pull request #725 from bartvde/gpx

Implement GPX parser (read/write). (r=@fredj)
implement review comment by @ahocevar
Merge pull request #734 from bartvde/xml-ie9

Fix XML serialize and xml_eql in IE9 (r=@ahocevar)
Dispatch an error on Geolocation failure