change rdoc link target.
Merge pull request #10 from sho-h/change-rdoc-link

change rdoc link target.

ruby-doc.org -> docs.ruby-lang.org
support version branching in BitClust::FunctionReferenceParser::parse_file
Merge pull request #11 from sho-h/add-capi-version-branch

support version branching in BitClust::FunctionReferenceParser::parse_file