add gemspec file and change readme to rdoc format.
update README.doc
add rspec test suite.
add spec and code for edge class.
Merge branch 'edge' into develop
add plain node class.
add node class and specs.
Merge branch 'node' into develop
add graph classes and incomplete spec file.
add examples.
bump version number to 0.0.1
hotfix: remove useless capture function in rspec helper.
bump version to 0.0.2