Add pre-commit to the repo

This adds pre-commit which can be used to enforce consistent style
and common errors (like committing large files)

.pre-commit-config.yaml

@@ -0,0 +1,19 @@
+---
+repos:
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v2.4.0
+    hooks:
+      - id: check-added-large-files
+      - id: check-yaml
+        args:
+          - --allow-multiple-documents
+      - id: trailing-whitespace
+      - id: end-of-file-fixer
+      - id: check-merge-conflict
+  - repo: git://github.com/dnephin/pre-commit-golang
+    rev: v0.3.5
+    hooks:
+      - id: go-fmt
+      - id: go-imports
+      # - id: gometalinter
+      # - id: golangci-lint