updated README with note on safari storage bug.
Merge pull request #149 from andygup/troubleshoot_safari_bug

updated README with note on safari storage bug.
added getExtentBuffer and getTileUrls to offlineTileEnabler
updated README
fixed minor bugs in new helper methods
tweaked and renamed getTileUrls to getTileUrlsByExtent to prevent confusion with getTileUrl override
updated spec to include two new helper methods
updated readme to reflect change of getTileUrlsByExtent name
validate if urls are actual urls
removed getTileUrl() call
added assert statement to detect if img is undefined
Merge pull request #152 from andygup/new_methods

Added two helper methods to offlineTileEnabler
added gruntfile and package.json for appcache generator
added gruntfile for grunt-manifest
added gitignore
added utils/appCacheManager.js - helper lib
added sample manifest.appcache file
initital commit
added images subdirectory to samples to make appcache easier
generated new appcache. Mostly working. one 404