Add support for the prince-of-space Java formatter

[agustafson]

prince-of-space is a Java code formatter (JavaParser-based) with configurable indent style/size, line length, wrap style, closing-paren placement, trailing commas, and Java language level.

I'd like to add first-class support for it alongside the other Java formatters (palantir-java-format, google-java-format, etc.), with:

• lib: a new PrinceOfSpaceStep using the standard JarState + reflection glue pattern, in a new princeOfSpace source set
• plugin-gradle: a princeOfSpace() / princeOfSpace(version) DSL on the java {} extension
• plugin-maven: a <princeOfSpace> step configuration
• Tests, README docs, and CHANGES.md entries for all three modules

I have a draft implementation ready — PR to follow.