Support for Eden trace viewer, and for ghc-7.8.2 thread stop event

These patches introduce Eden trace viewer events to ghc-events baseline, which were previously maintained as a drop-in replacement package ghc-events-parallel. We mailed previously about merging the two versions.
Also, the new version fixes decoding of ghc-7.8.2 thread stop events.
Replacing mtl by transformers comes in a separate pull request.

/ Jost