Improve query script output

[jtibshirani]

Small improvements to the Zoekt query script:

• Switch to chunk matches instead of line matches to better represent
  Sourcegraph search
• Make the results more readable by pulling out the filename and limiting the
  number of matches

[keegancsmith]

LGTM, but we should hide these changes in behaviour behind a flag. The zoekt cmd is used by some people for local search, so they probably expect grep like output.

[jtibshirani]

Oh oops, I thought this was just a testing script :) Instead of using a feature flag, what would you think of forking this into a script for testing ranking? I'd expect the changes to add up -- using FlushWallTime, the ability to pass a list of queries + relevant files and calculate an aggregate score, etc.

[keegancsmith]

Yeah lets add a new command.