Introduce new DocBuilder abstraction fo bundling RecursiveDocGenerators with their DocGenerator

o Remove SimpleRecDocGen
o Remove NestedDocGen
o Rename RecursiveDocGen to NestedDocGen
Convert doc builders to be easily chainable as a flattened list of partial functions by introducing DocBuilderChain
Label support for astExpressionDocBuilder
Rename pprint.docGen => pprint.docbuilders
Add pages for forcing use of line breaks in a group
Add logicalPlanDocBuilder
Replace string visitor with pprint
Add support for logical connectives and numerical comparisons to astExpressionDocBuilder
Reorganize Doc helpers for breaks and remove some dead code
Fix query graph indentation
Reorganize Pretty trait and Doc helpers
pprinting of ast literals and function invocations
Change quote{String|Char} to match up with Cypher manual
Add prettyDocBuilder for allowing instances to render themselves directly
Merge pull request #2431 from boggle/pp

pprint: cleanup, docgen caching, logical plans