Add support for pending specs.

Any describe block without its definition function is pending:

      describe("pending describe");
      xdescribe("pending excluded describe");
      ddescribe("pending exclusive describe");

Any it block without its definition function is pending:

      it("pending it");
      xit("pending exlcluded it");
      iit("pending exclusive it");
update README to enable the syntax highlighting of Dart code samples
update README to cover pending specs
add information about pending specs to SuiteInfo
Merge pull request #25 from vsavkin/pending_specs

Pending specs