Also do following improvements:
- show proper sublinter name for megacheck sublinters
- refactor and make more simple and robust megacheck
merging/optimizing
- improve handling of unknown linter names in //nolint directives
- minimize diff of our megacheck version from the upstream,
https://github.com/golang/go/issues/29612 blocks usage of the upstream
version
- support the new `stylecheck` linter
- improve tests coverage for megacheck and nolint related cases
- update and use upstream versions of unparam and interfacer instead of forked
ones
- don't use golangci/tools repo anymore
- fix newly found issues after updating linters
Also should be noted that megacheck works much faster and consumes less
memory in the newest release, therefore golangci-lint works noticeably
faster and consumes less memory for large repos.
Relates: #314
1. Support unparam linter and fix found issues
2. Replace forked mvdan.cc/lint and mvdan.cc/interfacer with the
upstream ones
3. Minimize forked megacheck: move the most of it's code to this repo
4. Use golang.org/x/tools/go/ssa import path instead of custom fork
paths
5. In golang.org/x/tools/go/{ssa,callgraph} use changed code from
honnef.co/go/tools
6. Add megacheck.check-unexported option: it found some issues in
the repo, fixed them all
