goimports for import rewritting
golangci-lint as the configurable linting swiss army knife.
These tools are recorded in [tools.go](https://github.com/golang/go/wiki/Modules#how-can-i-track-tool-dependencies-for-a-module). This records
them as a dependency to make sure we're all using the same tool versions.
To make sure this project's tool's versions don't stomp over versions
from other projects, they are installed in ./.tools, which is
.gitignored.
goimports was run and fixed up a single file:
plugin/httptrace/httptrace.go
I prefer to group local packages below external packages, hence the use
of goimports -local option.
.golangci.yml contains nothing but an incomplete set of defaults ATM.
I expect those to change over time though. ;-)
To use, run:
$ make precommit
Fixes#15
