Keep protobuf fields on one line

[ethanfrey]

Is your feature request related to a problem? Please describe.

With the use of prototool format in the Makefile, we are getting code like this in the *.proto files:

orm.VersionedIDRef electorate_ref = 5 [
    (gogoproto.customname) = "ElectorateRef",
    (gogoproto.nullable) = false
  ];

The problem here is that these gogoproto.* directives are custom to go and will choke any compiler for other languages. The current iov-core protobuf build chain was stripping out all directives... but it only works when on one line:

sed -ie 's/ *\[[^]]*\];/;/g' "$outfile"

And multiline sed looks like a nightmare: https://unix.stackexchange.com/a/26290

Describe the solution you'd like

As discussed here: https://github.com/iov-one/weave/pull/616/files#r282859931 please configure prototool format to leave long lines. Then I will validate it compiles well with iov-core scripts (and adjust them if needed)

Describe alternatives you've considered

Dropping sed and using perl for string replacement... but I would really like to have the most supported *.proto files possible.

@husio suggested we just do all pre-processing ourselves and produce one protobuf file per command (eg. bnsd, bcpd, etc) that can easily be imported by iov-core. This would remove a script in iov-core that grab these out and clean them up, and make the interface more portable. (Some related commented in #187 which we just did for docs)

Additional context
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