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
implement @tschaub's suggestions for the LIKE function
implement @tschaub's suggestions for ieq and ineq
merge with master - solving conflicts
change _expression reader
trim the string before passing it off to ol.expr.parse
make sure the _expression reader can deal with combined propertyname and literals
remove accidentally committed swap file
Building an expression with constructors instead of ol.expr.parse
Fix opacity in createFromString
Merge pull request #902 from twpayne/fix-color

Fix opacity in createFromString
Parse distance as a number
Remove special write-only handling for dates
Test names and instanceof checks
Proper use of expect
Correct use of expect with spies
Merge pull request #3 from tschaub/bartvde-ogcfilter2

Suggestions for filter encoding