Update android tests
All tests passing on master branch of appium
Log warning when methods are added to Selenium
Merge pull request #133 from DylanLacey/master

Log warning when methods are added to Selenium
Add context switching

`current_context` returns the current context
`current_context=` sets the current context
`available_contexts` returns an array of available contexts
`within_context` takes a context and a block, and switches to the
context for the duration of the block
`switch_to_default_context` switches to the default context
Update docs with context handling
Add uiautomat[ion|or] locators