Add `live_server` fixture

Useful with Selenium and headless browsers.
Add base test suite for a live server
Configurable port to run live server via app config
Add index route to test application

This endpoint uses to start :class:`LiveServer` instance with minimum
waiting timeout.
Add option to pytest cli to set port of live server

Option passed via command line overrides the option passed
via application config.
Add method to make complete url for server

Method `url` looks more useful then `url` property.
Make `url_for` works as expected when live server is running

Explicitly set application ``SERVER_NAME`` for test suite and restore original
value on test teardown.
Add docstring for `live_server` fixture
Add note about `live_server` to pypi page
Use 5000 as default port for live server

For better compatibility with Flask-Testing.
Update version number
Ensure the server name is rewritten
Fix format of external link for pypi page description
Merge pull request #12 from vitalk/support-live-server

Support live server. Closes #11.