cleanup: replaced all 'Entry' type parameters with just 'E'
cleanup: replaced all 'Elem' type parameters with just 'L'
cleanup: replaced all 'Seq' type parameters with just 'S'
cleanup: replaced all 'Parallel' type parameters with just 'P'
better comments on the type parameters and in general
fixed typo + formatting
added partial support for proof meta-information (ProofInfo)

Supporting PP tree->graph conversion to collect proof meta-info. Still need to do graph->tree.
refactoring PProcessGraph to avoid re-stating type parameters everywhere
better comments
initial implementation of ProofInfo preservation during attempt extension
forgot to exclude the consumed info element
fixed info accummulation
Merge branch 'graph-info-data'