refactor plugin
plugin returns a public instance. public instance with settings API
add zoom methods to public instance
start browserifying
Move some functionality into modules. Closes #36

This is just a small granularization. Even more methods may be exported into modules.
All the functions that require instance object remain in main file.
Mouse events handlers may be moved into a separate module but in this case either
methods should be called with plugin instance context, or plugin instance should be
passed as an argument.
add back control icons
add pannign ability
add onPan event handler. closes #20
add getPan and getZoom to API
Update README.md
update demos
update zoom funcitons. public getPan and getZoom
fix zoom in and out
bump version 2.0.0
Merge pull request #41 from bumbu/refactor

Refactor plugin, bump to version 2.0.0