Change method names in Spring convenience class

Users will find it more friendly and easier to remember if all they
need is a static import and a method called "spring" (as opposed to
having to remember 2 method names, one of which is "run" which could
mean anything).

E.g.

ratpack {
   handlers {
     register spring(SampleSpringBootApp)

     handler("foo") { String msg ->
       render msg
     }
   }
 }
Merge pull request #445 from dsyer/feature/spring-static

Change method names in Spring convenience class
Inline the static factories for functional type companions.
Lambda-ize.
Fix bad references.
Fix Javadoc style after Java 8 upgrade.
Javadoc fixes.
Javadoc tweaks for Spring support.
Fix manual snippets.
More Javadoc style fixes.
Minor formatting.
Implement default methods for Registry.
Some workarounds for JaCoCo issues with Java 8.
Javadoc style fix.
Some doc improvements.
Javadoc style fix.
Tweak appveyor build
Tweak appveyor build.
Tweaks to cloud CI test configuration.
Fix license header.