Render full window size if document has no height

When rendering a screenshot with `:full => true` on a document which has
a height of zero, the call fails silently with no screenshot being
created.  This situation can occur with pages that use absolute or fixed
positioning for all content, for example.

Changed to use the `documentElement`'s `clientHeight` & `clientWidth` as
a fallback, which will result in screenshots the size of the viewport in
that case.
Merge pull request #452 from kevinmcconnell/render-full-with-no-document-height

Render full window size if document has no height
added submit event triggering
Merge pull request #459 from khodzha/form_submit

Added submit event triggering
Update links to new repo URL
Merge pull request #487 from tjschuck/repo_url_updates

Update links to new repo URL
use protocol-relative URL

instead of fixed URI scheme (http:) to stop the message: "The page
*.html ran insecure content"
Merge pull request #491 from sunaot/protocol-relative-link

use protocol-relative URL to stop warnings on https pages
Don't alter focus with send_keys if we're already in the target element.

If the click event is fired on the target element, then the caret
position that was previously set by, e.g.,

  send_keys(:Left)

is lost. This addresses that by first checking if the target element
already contains the current selection, meaning we have focus within the
target element and don't need to first give it focus.

Fixes #493.
Use rbx-2 in travis.yml.
Merge pull request #494 from aprescott/send-keys-focus

Don't alter focus with send_keys if we're already in the target element
Add a change log entry for #493 [ci skip]
Add fresh links to README [ci skip]
Use the same code style for specs
Ensure exit code is propagated.

If `stop` raises and rescues an exception, $! becomes nil. Seemingly impossible
to reproduce in a unit test. For more information, see
https://github.com/teampoltergeist/poltergeist/issues/497

Fixes #497.
Merge pull request #498 from botandrose/fix_exit_code

Ensure exit code is propagated.
We'll have to implement features provided by capybara >= 2.3
Close dup'ed fd after using
Show off the latest release
Initial pack of changes for capybara 2.3 compatibility