Update README.md
do not require full WS2-URL - fixes #2
juse path.Join to concat path
adds inc param to lookup requests
fixes testing
first attempt towards supporting relations
package doc++
update README

fix example
don't overwrite RelationMap
skip elem rather than returning an error
fix: don't overwrite WS2RootURL
mv RelationMap -> TargetRelationsMap
variadic inc argument for lookups, fix doc
fix unmarshaling of relations
add convenience method to filter relations by type