Write a tool to summarize w directory data

[danielmai]

When an Alpha restarts it replays entries from the write-ahead log in the w directory. We need to be able to inspect the entries in the w directory to understand what would be replayed. This should be a tool that works like dgraph debug and prints out for each WAL entry the type (e.g., a mutation, commit, etc.), the size of each entry, the total number of entries, and so on.

[codexnull]

Would it make sense to add that as a feature to dgraph debug rather that writing a new tool?

[manishrjain]

Yes, in dgraph debug. I'm working on this.

[manishrjain]

Merged #3319 .