Convert PrettyParams to a case class

Add monocle lenses for PrettyParams
Update PrettyParamsSpec to use s2 macro
Add dropNullKeys pretty print option

If true object keys with null values will not be present in the output
Split comma into arrayComma and objectComma

Split pretty print commaLeft and commaRight options into array and
object specific versions
Add lrbracketsEmpty pretty print option

Determines the spacing to use between array brackets when the array is
empty