Makefile: add codespell target

Added codespell target for checking typos in repo.
Added codespell config file.

Author: vr009

.codespellrc

@@ -0,0 +1,5 @@
+[codespell]
+skip = */testdata,./LICENSE,./datetime/timezones.go
+ignore-words-list = ro,gost,warmup
+count =
+quiet-level = 3

Makefile

@@ -134,3 +134,8 @@ fuzzing:
 	@echo "Running fuzzing tests"
 	go clean -testcache
 	go test -tags "$(TAGS)" ./... -run=^Fuzz -v -p 1
+
+.PHONY: codespell
+codespell:
+	@echo "Running codespell"
+	codespell