Firefox 18+ supports String#startsWith, String#endsWith
Optional position argument

Added optional position argument to `String#startsWith`, `String#endsWith`, as described in https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/String/startsWith and https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/String/endsWith.
Documented new arguments and examples.
Updated unit tests
Add documentation example for `Element#clone.`
Merge pull request #96 from victor-homyakov/patch-33

Use native `String#startsWith` and `String#endsWith` if present. Turn existing implementation into a true polyfill.
Merge branch 'master' of github.com:sstephenson/prototype
Add polyfill information to documentation for `String#startsWith` and `String#endsWith`.
Merge pull request #98 from kir/master

Ensure that '+' is correctly deserialized in `String#toQueryParams`.
Fix an issue with a capability check causing an error in IE 10.
Merge branch 'master' of github.com:sstephenson/prototype