add convenience function to extract translations

Adds phase awareness in this function. Closes #349.
gtlua: add feature_node:extract_and_translate_sequence()
reintroduce non-mandatory joining
gtlua: make join a parameter again
gtlua: extend documentation of FeatureNode bindings
move around Lua method implementations, add __eq and __tostring

Closes #352.
add simple testcase for phase aware translation
update test cases with multi-CDS situations
small fixes to make gcc happy
improve performance of merge stream

Closes #348.
Merge pull request #354 from satta/merge_faster

improve performance of merge stream
Merge pull request #353 from satta/phases

add CDS phase aware translation and Lua improvements
gtlua: implement first version of custom visitor
gtlua: implement first version of custom stream
add test cases for custom streams
add tests for custom visitor
improve error checking in gt_inlineseq tools
Merge pull request #357 from satta/lua_customstreams

Add Lua custom stream and visitor support
Merge pull request #358 from satta/inlineseq_errorcheck

improve error checking in gt_inlineseq tools