First cut at Ysld module.
Implemented Ysld to GeoTools parser
Fixing NaN comparison, using Double.isNan, rathern than !=
Fixing pom name
Setting version to 2.6-SNAPSHOT
Added geoserver dependency, created app context with style handler.
refactored packages into geotools/geoserver packages
reorganized module into geotools and geoserver components
Support for parsing partial rules and symbolizers.
Parsing updates, moving away from low level api.

- Using Yaml.load to pre-parse to support anchors and references
- Created YamlObject, YamlMap, YamlSeq object hierarchy, removed YamlObj
Updated ysld mime type
Removed YamlObj class
Ensuring external graphic not added prematurely.
Added Colors containing map of named colors.

- Refactored some test cases.
Implemented YamlObject.toString()
Commenting out printing of transformed object
Added overloaded expression method to return null when string can't be parsed as cql
Added support for parsing rendering transformations
Removing camel-case symbolizer option conversion
Some docs for Ysld