New development error page styles

Closes #448
Add test coverage for configuration module
Merge branch 'master' of github.com:ratpack/ratpack
Experiment with configurable modules.
Upgrade to Guice 4 beta for Java 8 compatibility.
Remove the varargs methods from BindingsSpec.
Don't add the Groovy templating module by default.
Block guice from depending on guava.
Block guava here too.
Add left()/right() aliases to Pair.
Docs for configurable module.
Detach the HTTP URL builder from request spec.
Some more convenience to with.
Some tweaks to URL building.
Add convenience for get requests with no configuration.
Fix escaping issue with path segment patterns.
Merge pull request #463 from robzienert/new-error-styles

New development error page styles
Fix GitHub API requests for site.
Provide a throttle for generic operations.

Closes #449.
Upgrade to latest RxJava.