Add unit test for case-sensitivity

[andrejpavlovic]

Setting XPath to use case-sensitive vs case-insensitive seems to work for node names. Need to create unit tests for this as well as attribute names, and any other node names.

Wherever .nodeName is used, need to take case-sensitivity into account.

XPath should be case sensitive, but HTML documents aren't, so we have made XPathJS not case sensitive by default.