Integrate 'pre-commit'

Helps me avoid simple style issues.

Signed-off-by: Stephen Finucane <stephen@that.guru>

Author: stephenfin

.pre-commit-config.yaml

@@ -0,0 +1,10 @@
+repos:
+- repo: https://github.com/pre-commit/pre-commit-hooks
+  rev: v2.3.0
+  hooks:
+  - id: check-executables-have-shebangs
+  - id: check-merge-conflict
+  - id: check-yaml
+  - id: end-of-file-fixer
+  - id: flake8
+  - id: trailing-whitespace