Add precommit hooks & tox env to enforce code structure, add azure pipelines

Instead of leveraging hound & travis, add an option for azure pipelines,
which may replace the former in the future.

This also streamlines the contributing guidelines by:
* Adding pre-commit hooks to run isort, black, flake8, mypy
* Adding lint environment to allow checks to be run `tox -e lint`

This also contains a major cleanup to the SmartStrip handling which was due.
After seeing #184 I thought I should push this in as it is for comments before the codebase diverges too much.

.pre-commit-config.yaml

@@ -1,6 +1,24 @@
 repos:
--   repo: https://github.com/python/black
-    rev: stable
-    hooks:
-    - id: black
-      language_version: python3.7
+- repo: https://github.com/python/black
+  rev: stable
+  hooks:
+  - id: black
+    language_version: python3.7
+
+- repo: https://github.com/pre-commit/pre-commit-hooks
+  rev: v2.3.0
+  hooks:
+  - id: flake8
+    additional_dependencies: [flake8-docstrings]
+
+
+- repo: https://github.com/pre-commit/mirrors-isort
+  rev: v4.3.21
+  hooks:
+  - id: isort
+
+- repo: https://github.com/pre-commit/mirrors-mypy
+  rev: v0.740
+  hooks:
+  - id: mypy
+#    args: [--no-strict-optional, --ignore-missing-imports]