Move more functionality into internal/build/build.go

and use make targets in CI, pass flag spec YAML through yq

includes result of running `make v2approve`

Makefile

@@ -4,8 +4,10 @@
 # are very important so that maintainers and contributors can focus their
 # attention on files that are primarily Go.
 
+GO_RUN_BUILD := go run internal/build/build.go
+
 .PHONY: all
-all: generate vet tag-test test check-binary-size tag-check-binary-size gfmrun v2diff
+all: generate vet tag-test test check-binary-size tag-check-binary-size gfmrun yamlfmt v2diff
 
 # NOTE: this is a special catch-all rule to run any of the commands
 # defined in internal/build/build.go with optional arguments passed
@@ -13,28 +15,28 @@ all: generate vet tag-test test check-binary-size tag-check-binary-size gfmrun v
 #
 #   $ make test GFLAGS='--packages cli'
 %:
-	go run internal/build/build.go $(GFLAGS) $* $(FLAGS)
+	$(GO_RUN_BUILD) $(GFLAGS) $* $(FLAGS)
 
 .PHONY: tag-test
 tag-test:
-	go run internal/build/build.go -tags urfave_cli_no_docs test
+	$(GO_RUN_BUILD) -tags urfave_cli_no_docs test
 
 .PHONY: tag-check-binary-size
 tag-check-binary-size:
-	go run internal/build/build.go -tags urfave_cli_no_docs check-binary-size
+	$(GO_RUN_BUILD) -tags urfave_cli_no_docs check-binary-size
 
 .PHONY: gfmrun
 gfmrun:
-	go run internal/build/build.go gfmrun docs/v2/manual.md
+	$(GO_RUN_BUILD) gfmrun --walk docs/v2/
+
+.PHONY: ci-ensure-mkdocs
+ci-ensure-mkdocs:
+	$(GO_RUN_BUILD) ensure-mkdocs --upgrade-pip
 
 .PHONY: docs
 docs:
 	mkdocs build
 
-.PHONY: docs-deps
-docs-deps:
-	pip install -r mkdocs-requirements.txt
-
 .PHONY: serve-docs
 serve-docs:
 	mkdocs serve