* save state

* snapshot update works

* save state

* snapshot migrator

* tx test

* save state

* migrations stages refactor

* refactor snapshot migrator

* compilation fixed

* integrate snapshot migrator

* goerli sync headers

* debug async snapshotter on goerly

* move verify headers, remove experiments, fix remove old snapshot

* save state

* refactor snapshotsync injection

* fix deadlock

* replace snapshot generation stage logic to migrate method

* change done for body snapshot

* clean

* clean&&change deleted value

* clean

* fix hash len

* fix hash len

* remove one of wrap methods, add remove snapshots on start

* add err check

* fix shadowing

* stages unwind order debug

* matryoshka experiments

* steam test

* fix build

* fix test

* fix lint

* fix test

* fix test datarace

* add get test

* return timeout

* fix mdbx overlap

* fix after merge

* change epoch size

* clean todo

* fix

* return testdata

* added return from sndownloader gorutine

* fix review comments

* Fix

* More info

Co-authored-by: Alex Sharp <alexsharp@Alexs-MacBook-Pro.local>

* build: upgrade to golangci-lint v1.27.0

* build: raise lint timeout to 3 minutes

* build: upgrade golangci to 1.22.2

* .golangci.yml: don't fail on asset deadcode

* build: use golangci-lint

This changes build/ci.go to download and run golangci-lint instead
of gometalinter.

* core/state: fix unnecessary conversion

* p2p/simulations: fix lock copying (found by go vet)

* signer/core: fix unnecessary conversions

* crypto/ecies: remove unused function cmpPublic

* core/rawdb: remove unused function print

* core/state: remove unused function xTestFuzzCutter

* core/vm: disable TestWriteExpectedValues in a different way

* core/forkid: remove unused function checksum

* les: remove unused type proofsData

* cmd/utils: remove unused functions prefixedNames, prefixFor

* crypto/bn256: run goimports

* p2p/nat: fix goimports lint issue

* cmd/clef: avoid using unkeyed struct fields

* les: cancel context in testRequest

* rlp: delete unreachable code

* core: gofmt

* internal/build: simplify DownloadFile for Go 1.11 compatibility

* build: remove go test --short flag

* .travis.yml: disable build cache

* whisper/whisperv6: fix ineffectual assignment in TestWhisperIdentityManagement

* .golangci.yml: enable goconst and ineffassign linters

* build: print message when there are no lint issues

* internal/build: refactor download a bit