Implement missing API functions and update docs

Implements:
- element.getSize()
- driver.setLocalStorageKey(key, value)
- driver.getLocalStorageKeys()
- driver.clearLocalStorage()
- driver.getGeolocation()
- driver.setGeolocation(location)

Updates:
- Added a simple code example for new users
- Added getLocation() and getLocationInView() to docs because they were already implemeted
Can we `var` this up?