Fix golangci#331: fix errcheck "ignore" config directive.

Make tests for "ignore" and "exclude" directives.
Mark all hidden command-line options as deprecated.

Fix golangci#318: better validate linters and help commands

remove unnecessary command from Dockerfile

fix golangci#277, fix golangci#260: fix crash

Fix crash because of parallel access to ssa.Program

Fix golangci#282, fix golangci#209: revert goimports commit

ed64e33c8c8bc9a919e2b85a1a08225b5ae59d70. Also add tests
for local mode of goimports and do refactoring of tests.

dev: fix tests

Fix false positives with unused identifiers

Issue golangci#265: don't report unused warning when an identifier is
used only in tests.

Fix golangci#261: build-tags fix for package loader

docs: write about Atom integration

update golang.org/x/tools