fix: only trap EntityKeyNotFoundException in DEntity methods

other methods such as ClassCastExceptions were being suppressed in SchemaDEntityOps methods
Remove overloads on SchemaDEntityOps .read and .readOpt

it’s just plain confusing ;) and not very valuable
add SchemaDEntityOps .idView and .idViews

rewrite (get)idView(s) in terms of read methods
quick test of idView in DatomicMappingSpec
document SchemaDEntityOps
Merge pull request #44 from pellucidanalytics/fix/DEntityOps

Fix exception handling in SchemaDEntityOps and refactor methods on DEntity