feat: requires-python (#536)

* feat: requires-python

refactor: updating to current proposal

fix: add tests and fix a few issues

docs: Update mostly from @joerick

docs: update README from readthedocs

* refactor: pull out config file reading

* fix: always assume highest Python patch version

* refactor: try new design

* refactor: function and bump MyPy to 0.800

* fix: tighten AST to call only, add docs

* fix: address review points from @joerick

.pre-commit-config.yaml

@@ -24,12 +24,16 @@ repos:
     args: ["--line-length=120"]
 
 - repo: https://github.com/pre-commit/mirrors-mypy
-  rev: v0.790
+  rev: v0.800
   hooks:
   - id: mypy
-    files: ^(cibuildwheel/|test/|bin/projects.py|bin/update_pythons.py|unit_test/)
-    pass_filenames: false
-    additional_dependencies: [packaging, click]
+    exclude: ^(bin/|cibuildwheel/resources/).*py$
+    additional_dependencies: [packaging]
+  - id: mypy
+    name: mypy 3.7+ on bin/
+    files: ^bin/.*py$
+    additional_dependencies: [packaging]
+    args: ["--python-version=3.7", "--ignore-missing-imports", "--scripts-are-modules"]
 
 - repo: https://github.com/asottile/pyupgrade
   rev: v2.7.4