Maps: Added demos.
Optimized performance by caching results for getBBox for numbers, since numbers are monospaced and the same bounding box applies to any number of the same character length and the same font family and font size. Also, don't delete cached bounding box on word wrap when there is only one word. These two optimizations improved rendering times by 15% on Chrome and Firefox using our benchmark tests. Relates to #2525.
Added demo for axis.showEmpty option.