remove NamespacePrefixMapperImpl in favor of specifying NS in package-info.java
- the interface NamespacePrefixMapper lies in an internal package
- depending on the compiler settings, this leads to a compilation error (if access to rt.jar-internal packages is disallowed)
- see https://issues.apache.org/jira/browse/SIS-74 for a related discussion on exchanging the NamespacePrefixMapper-based approach
Merge pull request #34 from ftes/remove-namespace-prefix-mapper

remove NamespacePrefixMapperImpl in favor of specifying NS in package-info.java