Add R.pathEq function.

R.pathEq determines whether the given, possibly nested, path of an
object has a  specific value according to strict equality ('===').

This function is implemented by passing the arguments to R.eq and using
R.path.
Updated documentation

Changed the documentation of R.pathEq to align more with R.path.
Merge pull request #436 from TheLudd/master

Add R.pathEq function.