Added setLegacy(true) to GML2 Encoding

I'm not sure when it changed, but in version 10-RC2 the GML class requires a "legacy" flag to be set to true before encoding features to GML2.

I've added code to set the flag to true, at least for the "full example"
Updated GML2 encode example: out2 -> xml

The example uses "encode2.encode(out2, collection);", but "out2" is not a defined variable. I assume that it was supposed to be "encode2.encode(xml, collection)" since the OutputStream "xml" is never written to.
Updated GML2 encode example to use List<SimpleFeature> to accumulate features

According to the feature tutorial, FeatureCollection objects should not be treated as immutable views, and so the add method was deprecated. I've updated the code to instead create a List<SimpleFeature> and then convert that list into a SimpleFeatureCollection where needed.
Expanded the amount of code included in the transform example

The amount of code included from "//transformExample start" to "//transformExample end" was previously insufficient to demonstrate how the prefixes should be structured or the collections created. It resulted in code being included in the Geometry documentation which did not build. I have modified the code to use an immutable FeatureCollection view, and have expanded the amount of code used in the example. The Geometry documentation will now have code that builds.
Changed tabs to spaces
Tried using a relative path to get the literalinclude
Update geometry.rst
Merge pull request #275 from dewthefifth/patch-3

Added setLegacy(true) to GML2 Encoding