Added generic LRU cache and implementation for resource cache.

Updated ResourceIndex to use these LRU caches instead of the old
implementations.
Increased default resource cache limit
Documentation updates

Added a note about the new BrightstarDB.ResourceCacheLimit option.
Chagned the toctree for the Developing_With_BrightstarDB file so that it
is visible.
Added a list of new features in develop branch to the Whats_New file.
Merge branch 'feature/lruresourcecache' into develop