Support for verifying textarea element text

Addresses the issue described in #167.
Merge pull request #185 from emanlove/master

Added 'Get Window Size' and 'Set Window Size' keywords.
Merge pull request #231 from emanlove/master

Added code and tests to check for non-existing select items from list.
Merge pull request #232 from emanlove/master

Fixed bad browser name raising AttributeError.

Fixes #157
Merge pull request #168 from stevejefferies/master

Support for verifying text entered into textarea elements
Merge pull request #233 from emanlove/master

Added tests for new textarea keywords.
Removed note about current issue with Firefox.

This information should be within the release notes or wiki as the keyword
documentation does update until a release and the status with Firefox might
have changed inbetween builds/documentation updates.