Allow the name of the StatsdInput to use to be specified in the StatFilter config in
case it's not the default.
Merge branch 'features/statfilter-configable-input-name' into features/doc-string-audit
Add stat_filter.go doc strings.
`statsd_input_writer.go` => `statsd_input.go`, plus update doc strings.
Use FilterRunner.LogError instead of hand-rolled, fix couple of doc string typos.
Slight doc string tweaks for whisper.go.
Merge branch 'features/doc-string-audit' into dev