Deprecate GtFeatureStream, replace with GtFeatureInStream

Simply doing a typedef of gt_feature_in_stream_new to gt_feature_stream_new was gave the desired functionality, but did not generate the desired (HTML) documentation. Thus the trivial constructor implementation.
Merge branch 'master' of https://github.com/genometools/genometools
Merge branch 'master' of https://github.com/genometools/genometools
Merge pull request #68 from standage/master

Deprecate GtFeatureStream, replace with GtFeatureInStream