Update to v0.29.1

Update README

Bump version to v0.29.0-rc.1

Add ElementQuery::single()

Fix clippy warning

Fix lifetime on ElementQuery::first_opt()

Major refactor to improve ease of maintenance

- Move the session to an async task, using channels.
- Remove WebDriverCommands trait, and add methods
directly to SessionHandle.
- Store SessionHandle in WebDriver directly and remove GenericWebDriver.
- Pass a reference to SessionHandle to all elements and other structs
that make use of the session.
- Simplify ElementQuery slightly.
- Move all session handling to the session module.
- Update dependency versions.

Add select_by_xpath_condition() to SelectElement

Also add select_by_partial_text and select_by_exact_text methods to SelectElement

Improve in_new_tab check to make new tab more robust. Add doctest.

Add ability to add extensions to Chrome as well as other options