chore: add commitlint and husky (open-telemetry#128)

Change CONTRIBUTING.md
Resolves open-telemetry#117

Signed-off-by: Olivier Albertini <olivier.albertini@montreal.ca>

api/.commitlintrc.yml

@@ -0,0 +1,29 @@
+extends:
+  - '@commitlint/config-conventional'
+rules:
+  header-max-length: [1, 'always', 72]
+  type-enum:
+  - 2
+  - always
+  - - ci
+    - feat
+    - fix
+    - docs
+    - style
+    - refactor
+    - perf
+    - test
+    - revert
+    - chore
+help: |
+  **Possible types**:
+  `ci`:       Changes to our CI configuration files and scripts (example scopes: Travis, Circle CI, BrowserStack, SauceLabs)
+  `feat`:     Adds a new feature.
+  `fix`:      Solves a bug.
+  `docs`:     Adds or alters documentation. (example scopes: readme, worker, code_of_conduct, contributors)
+  `style`:    Improves formatting, white-space.
+  `refactor`: Rewrites code without feature, performance or bug changes.
+  `perf`:     Improves performance.
+  `test`:     Adds or modifies tests. (example scopes: functionals, unit-tests)
+  `revert`:   Changes that reverting other changes
+  `chore`:    No production code change. Updating grunt tasks etc;