Added Documentation for esri Namespace

Added documentation for these classes:
- esriRequest
- domUtils
- esriLang
- ProxyRule
- urlUtils
- Credential
- Graphic
- IdentityManagerBase
- IdentityManager
- InfoTemplate
- InfoWindowBase
- OperationBase
- Map
- ServerInfo
- SnappingManager
- SpatialReference
- TimeExtent
- UndoManager
- Units
Added Documentation for ArcGIS Namespace

- Completed documentation for classes in esri namespace.
- Completed documentation for all classes in ArcGIS namespace.
Added docs for esri.dijit.editing namespace

- Added documentation for esri.dijit.editing
Merge pull request #12 from AmrEldib/master

Added Documentation for esri Namespace
Nice Work !