Documentation updates and changes

Contains the following changes

* 857d44d65402cf470ef653cb6b6c52693b6d0438 Fixed documentation error with 'Press Key' keyword. Fixes #200.
* b90459ddbc2bf1f479aaadcb62d5cbeadbefe33b  Clarified documentation of XPath related keywords. Fixes #228.
* f8264afe0ec99f0ce9f5e09c15f85565bc8b6dda Added information on how to redirect console output when debugging. Fixes #147.