Fast infoContentMethod() implementation

This pull request dramatically improves the performance of `infoContentMethod()`, especially for long lists of GO terms.

`infoContentMethod_cpp()` function was rewritten to support lists of GO terms, so that the whole GO distance matrix is calculated by the single C++ call. Internally, infoContentMethod_cpp() now utilizes C++ maps and sets to avoid linear searches of GO terms etc.

I believe `wangMethod()` could also benefit for similar optimizations.