XPath function for accessing FeatureTypes from Schema

[jonherrmann]

This enhancement requires the implementation of a XQuery module that can be loaded by BaseX-based ETSs. The module should provide XPath functions for determining all FeatureTypes in an XML document by reading and analysing the associated schema.

1. A schema-element() function is required https://www.w3.org/TR/xpath20/#id-schema-element-test . Note: for performance reasons this is not implemented by BaseX itself.
2. The function call etf:feature-members( rootNodeOrSchemaLocation ) should return a sequence of all Feature member nodes in the Feature Collection.
3. The function call etf:feature-type-names( rootNodeOrSchemaLocation ) should return a sequence of strings with the names of all Feature Type names.

See also: http://docs.basex.org/wiki/Java_Bindings