Added linting and automatic formatting with prettier

[DiefBell]

• Added Prettier and script to prettify built JS. Auto-runs after building ts.
• Added ESLint and script to run it. Auto-runs before building ts.
• Added Husky pre-commit hooks to lint files before commits. Fails on ESLint errors AND warnings.
• Fixed the linting errors, which was largely use of let instead of const and use of explicit any.

Note: branched off branch for PR: #47