Add TypedSimilarity.
Add TypedSimilarity from latest master.
Use Specification in test.
Address Oscar's comments.
Update comments.
Only display custom counter message if there are custom counters.
Merge pull request #836 from azymnis/custom_counters_msg

Only display custom counter message if there are custom counters.
Merge pull request #833 from twitter/klin_typed_sim

Implementation of DISCO and DIMSUM algorithms.
Resolve doc generation errors in maple
Merge pull request #837 from danosipov/doc_fix

Resolve doc generation errors in maple
Merge https://github.com/twitter/scalding into develop