Register EXSLT namespaces by default (resolves #470)
Applying suggestions from previous comments
Update selectors documentation and tests
Fix typo error
Drop EXSLT strings and math extensions
Add warning in docs on performance when using EXSLT regexp functions
Rename "regexp" prefix to "re"
Merge pull request #472 from redapple/exslt

Register EXSLT namespaces by default (resolves #470)