LibGFF

This is an attempt to perform a simple "libraryfication" of the GFF/GTF parsing code that is used in GFFRead codebase. There are not many (any?) relatively lightweight GTF/GFF parsers exposing a C++ interface, and the goal of this library is to provide this functionality without the necessity of drawing in a heavy-weight dependency like SeqAn. Note: This library draws directly from the code in GFFRead and GCLib, and exists primarily to remove functionality (and hence code) that is unnecessary for our downstream purposes. In the future, it may be appropriate to just replace this library wholesale with GCLib.