Add 'make htmlview' and be consistent with our other Makefiles

Author: hugovk

Makefile

@@ -1,23 +1,29 @@
-CPYTHON_PATH               = ../cpython
+# You can set these variables from the command line.
+CPYTHON_PATH = ../cpython
+PYTHON       = python3
 PACKAGE_ABS_PATH = $(shell pwd)/$(shell find dist/python-docs-theme-*.tar.gz)
 
 
-.PHONY: html
-html: venv
-	cd $(CPYTHON_PATH)/Doc && \
-		make html
-
+.PHONY: help
+help:
+	@echo "Please use \`make <target>' where <target> is one of"
+	@echo "  venv       to create a venv with necessary tools at $(CPYTHON_PATH)/Doc/venv"
+	@echo "  html       to make standalone CPython HTML files"
+	@echo "  htmlview   to open the index page built by the html target in your browser"
 
 .PHONY: venv
 venv:
-	python3 -m pip install build
-	python3 -m build
+	$(PYTHON) -m pip install build
+	$(PYTHON) -m build
 	cd $(CPYTHON_PATH)/Doc \
 		&& make venv \
 		&& ./venv/bin/pip install $(PACKAGE_ABS_PATH)
 
-.PHONY: help
-help:
-	@echo "html:		default rule; run the \`venv\` rule, and also rebuild the CPython docs"
-	@echo "venv:		build the package, and install it into the virtual environment"
-	@echo "		at $(CPYTHON_PATH)/Doc/venv"
+.PHONY: html
+html: venv
+	cd $(CPYTHON_PATH)/Doc && \
+		make html
+
+.PHONY: htmlview
+htmlview: html
+	$(PYTHON) -c "import os, webbrowser; webbrowser.open('file://' + os.path.realpath('$(CPYTHON_PATH)/Doc/build/html/index.html'))"