Add Makefile and Markdown linter (#73)

* Add Makefile

* Update .gitignore to exclude venv

* Add requirements.txt for venv

* Add pymarkdown lint Github action

* Update .md from lint tool

* Update README with make commands

* Add linter config

Makefile

@@ -0,0 +1,47 @@
+DOCSDIR = docs
+VENVDIR = venv
+VENV = $(VENVDIR)/bin/activate
+MKDOCS_CONFIG ?= mkdocs.yml
+BUILDDIR ?= site
+TARGET = docs
+VALE_CONFIG = .vale.ini
+
+.PHONY: build install serve spelling vale-install 
+
+
+# If requirements are updated, venv should be rebuilt and timestamped.
+$(VENVDIR):
+	@echo "... setting up virtualenv"
+	python3 -m venv $(VENVDIR) || { echo "You must install python3-venv before you can build the documentation."; exit 1; }
+	. $(VENV); pip install $(PIPOPTS) --require-virtualenv \
+	    --upgrade -r requirements.txt \
+            --log $(VENVDIR)/pip_install.log
+	@test ! -f $(VENVDIR)/pip_list.txt || \
+            mv $(VENVDIR)/pip_list.txt $(VENVDIR)/pip_list.txt.bak
+	@. $(VENV); pip list --local --format=freeze > $(VENVDIR)/pip_list.txt
+	@touch $(VENVDIR)
+
+install: $(VENVDIR)
+
+build: install
+	. $(VENV); mkdocs build -f $(MKDOCS_CONFIG)
+
+lint-md: pymarkdownlnt-install
+	@. $(VENV); pymarkdownlnt --config .pymarkdown.json scan docs --recurse --exclude=./$(SPHINXDIR)/** $(SOURCEDIR)
+
+lint-md-fix: pymarkdownlnt-install
+	@. $(VENV); pymarkdownlnt fix --recurse $(DOCSDIR)
+
+pymarkdownlnt-install:
+	@. $(VENV); test -d $(VENVDIR)/lib/python*/site-packages/pymarkdown || pip install pymarkdownlnt
+
+serve: install
+	. $(VENV); mkdocs serve -f $(MKDOCS_CONFIG) --livereload
+
+vale-install: install
+	@. $(VENV);
+	@. $(VENV); find $(VENVDIR)/lib/python*/site-packages/vale/vale_bin -size 195c -exec vale --version \;
+
+spelling: vale-install
+	@echo "Running Vale against $(TARGET). To change target set TARGET= with make command"
+	@. $(VENV); vale --config="$(VALE_CONFIG)" --glob='*.{md,rst}' $(TARGET)