Refactor RaftJournal to user Mark instead of index
Merge pull request #71 from mgodave/journal-refactor

Refactor RaftJournal to user Mark instead of index
[wip] introduce POJOs API in core and move proto stuff to dedicated module

This compiles but is incomplete and certainly does not pass any test.
implement serialization of JournalEntry for RaftLog

* use plain old Java serialization
implement properly equals/hashcode/toString
convert from POJOs to Protos and back
added minimal package documentation
remove dependency on protoc and protobuf