Include python 3.8 i ci test runs & optimise CI and make config

Makefile

@@ -1,4 +1,6 @@
-help:               ##	- Show this help.
+.PHONY: help setup generate test types format clean plugin full-test check-style
+
+help:               ## - Show this help.
 	@fgrep -h "##" $(MAKEFILE_LIST) | fgrep -v fgrep | sed -e 's/\\$$//' | sed -e 's/##//'
 
 # Dev workflow tasks
@@ -6,16 +8,16 @@ help:               ##	- Show this help.
 generate:           ## - Generate test cases (do this once before running test)
 	poetry run ./betterproto/tests/generate.py
 
-test:               ##	- Run tests
+test:               ## - Run tests
 	poetry run pytest --cov betterproto
 
-types:              ##	- Check types with mypy
+types:              ## - Check types with mypy
 	poetry run mypy betterproto --ignore-missing-imports
 
-format:             ##	- Apply black formatting to source code
+format:             ## - Apply black formatting to source code
 	poetry run black . --exclude tests/output_
 
-clean:						  ## - Clean out generated files from the workspace
+clean:              ## - Clean out generated files from the workspace
 	rm -rf .coverage \
 	       .mypy_cache \
 	       .pytest_cache \
@@ -27,14 +29,14 @@ clean:						  ## - Clean out generated files from the workspace
 
 # By default write plugin output to a directory called output
 o=output
-plugin:             ##	- Execute the protoc plugin, with output writte to `output` or the value passed to `-o`
+plugin:             ## - Execute the protoc plugin, with output write to `output` or the value passed to `-o`
 	mkdir -p $(o)
 	protoc --plugin=protoc-gen-custom=betterproto/plugin.py $(i) --custom_out=$(o)
 
 # CI tasks
 
-full-test: generate ##	- Run full testing sequence
+full-test: generate ## - Run full testing sequence with multiple pythons
 	poetry run tox
 
-check-style:        ##	- Check if code style is correct
+check-style:        ## - Check if code style is correct
 	poetry run black . --check --diff --exclude tests/output_