Controls: added a ButtonControl (which is just LabelControl with some defaults)
LRUCache: fix an obscure multithreading problem
Color: add as() function
Docs: added compilation docs
Docs update.
Update docs/source/about.rst
Docs: add data.rst
Merge branch 'master' of github.com:gwaldron/osgearth

Conflicts:
	docs/source/about.rst
Decluttering: added a "max_objects" property for an upper limit on sorted drawables
Using OGROpen instead of OGROpenShared in OGR driver.
Merge branch 'master' of github.com:gwaldron/osgearth
Merge branch 'master' of github.com:gwaldron/osgearth

Conflicts:
	src/osgEarthDrivers/feature_ogr/FeatureSourceOGR.cpp
doc updates
Add ability to create arc or pie shapes in addition to circles or ellipses.
AltitudeFilter: fixed a bug that prevented javascript evaluation in altitude-offset and altitude-scale properties
Doc update
doc index: update
Update docs/source/user/index.rst
Update docs/source/user/index.rst
Docs update