jing/validator.nu not required by default. CLI instructions.

* Provided command line example. Fixes #3
* jing is not required to run xprocspec anymore. RNG validation can be enabled by setting the "step-available-rng" option to "true"
* the html5 test which requires validator.nu to load non-wellformed html is disabled by default, so that vanilla calabash with no additional libraries works for running the integration tests