Iterate functionality

Added the iterate() functionality to allow users to iterate through all available keys. (#283)

Thanks so much to @lu4 for the work on this release! Also to @thgreasi for his work on #329. And to @nolanlawson for his Blob fixes! Thanks to @af7 for their work on localStorage bugs.

1.2.10: Fixes for browserify and webpack users (#439)
1.2.9: Fixes localStorage iterate issues (#407 and #428)
1.2.4: Fixes WebKit blob issues (#381)
1.2.3: Fixes a bug with require (#378)
1.2.2: Fixes a bug with webpack (#340)
1.2.1: Fixes a bug with odd-length ArrayBuffer (#285)