Pretty-printing collections
Fix astDocBuilder to properly pretty print nested values
Add astStructureDocBuilder for printing both ast and structure
Various pretty printing tweaks

o Support ast.Parameter
o Disable astStructureDocGen for now
o Add Doc.noBreak
Extract core of perty function composition into separate bling package

o Improves error handling
o Replaces all of docbuilders and docgenerator types with new DocGen[-T]
o Temporarily disables Pretty, ast support
o Rename HasDocFormatter => DocFormatting
o Rename HasDocGen => DocHandler
o Prepares ast printing to use converter pattern (not hooked in)