added support for image service rendering rule

added test to spec for getter/setter functions
implemented getter/setter functions
updated _buildExportParams() to pass renderingRule if option is set
updated api reference page to include new option and getter/setter functions
added example page applying a hillshade to a DEM.

resolves #295
Add Rendering Rules page to examples TOC
Merge pull request #309 from tomwayson/issue-295

added support for applying a rendering rule to an image layer when exporting an image
added support for setting mosaic rule on export image

added test to ImageMapLayerSpec.js
implemented getter/setter functions and updated `_buildExportParams` in ImageMapLayer.js
updated api reference page
added example page using lock rasters to show only one raster in a mosaic
Merge pull request #310 from tomwayson/issue-298

added support for setting mosaic rule on export image
added support for image service nodata parameter

added tests to ImageMapLayerSpec.js
added getter/setter methods to ImageMapLayer.js
includes optional parameter to set noDataInterpretation when setting noData
updated api reference page w/ new option/methods

resolves #311
Merge pull request #313 from tomwayson/issue-311

added support for image service noData and noDataInterpretation parameters