Add parser for OGC Filter 1.0 and 1.1 (read/write)

This work is based on the ol.expr package by @tschaub.
It adds a few named expression functions to that package:

 * INTERSECTS, CONTAINS, DWITHIN, WITHIN (no client-side implementation as yet)
 * LIKE (like comparison with wildcard, singleChar and escapeChar)
 * IEQ (case-insensitive equality)
 * INEQ (case-insensitive non-equality)

It also adds a few extra parameters to the existing EXTENT function to be able
to deserialize and serialize all info (i.e. projection and property name).

Some changes were needed for the GML parser as well:

 * createGeometry function needed to be public
 * when parsing Box (GML2) and Envelope (GML3) also parse the srsName
 * fix up writing for Box and Envelope now that bounds is an array

Also added createDocumentFragment function to the XML parser. Implementation
is similar to OpenLayers 2.

Some addtional notes on the implementation:

 * PropertyIsBetween was implemented as an ol.expr.Logical with operator
   ol.expr.LogicalOp.AND and two ol.expr.Comparison instances with operator
   ol.expr.ComparisonOp.GTE and ol.expr.ComparisonOp.LTE
 * In OGC Filter And and Or can contain more than 2 sub filters, so this
   is translated into a hierarchy of ol.expr.Logical
address most of @tschaub's review comments, use dot notation where possible still needs to be done, and I have some questions on the _expression reader still
more dot notation
make filterMap_ static as proposed by @tschaub
Upgrade Font Awesome to version 3.2.1
Better label placement for polygons

Using the y-coordinate of the polygon's bounding box, this
simple algorithm intersects the polygon with the horizontal
center line of its bounding box. The x-coordinate of the label
point is the center of the longest segment of this intersection
that is inside the polygon.
implement @tschaub's suggestions for the LIKE function
implement @tschaub's suggestions for ieq and ineq
Adding TopoJSON externs
Adding TopoJSON parser
GeometryCollection as individual features
Transform arcs
Shared structure for crs transforms
Initial spec
Rendering 110m world TopoJSON
Exports
Tests for parsing world-110m.json
Update example
Slightly different style than other vector example
Missing requires in test and example lint