Update Readme section about Capybara.app

One of users [had a problem with it recently](http://stackoverflow.com/q/15665106/841064)
Merge pull request #1031 from abotalov/readme-update

Update Readme section about Capybara.app
Language police
Fix method comments
Merge pull request #1033 from tricknotes/fix-method-comments

Fix method comments
Removed duplicate option explanation

I guess the last one is enough.
Merge pull request #1036 from arr-ee/patch-1

Removed duplicate option explanation
Add stuff to history
Tagged 2.1.0.rc1
Depend on xpath ~> 2.0
tagged 2.1.0
Merge tag '2.1.0' into capybara-2.1