rework complaint reporting

instead of dumping everything straight to stdout, buffer it in a hash
first.
there are multiple advantages:
- in some cases, we'd get line-less complaints only after ones with
  lines, which would look funny. the buffering allows us to sort the
  output.
- different output formats will be easier to implement.
- the output code is cleaner, as it can hold the state more locally.

Change-Id: I0b558ecb58cf4d44a7efbd5a13a79349c55283f9
Reviewed-by: Orgad Shaneh <orgads@gmail.com>