chore: Improve git & npm workflow

[philippefutureboy]

Improve git workflow:

• Add commitizen + conventional changelog

Improve npm workflow:

• Remove yarn.lock, move to npm
• Add watch script
• Add dev script
• Add esm export
• Remove mockery devDependency

[philippefutureboy]

• Added Greenkeeper to the repository – Still not sure if enabled
• Updated AppVeyor CI – It was not working – Need to wait for some PR action to confirm if active

[philippefutureboy]

Note: Will have to update travis & appveyor configurations not to use yarn anymore

[philippefutureboy]

^ Moved that to greenkeeper/initial

[jacargentina]

I 've finished the code for the tests to work again. Great! 🎉