Introduce standardjs

[adaxi]

I suggest adding standardjs for code formatting. Main reasons are described at https://standardjs.com/

• No configuration. The easiest way to enforce consistent style in your project. Just drop it in.
• Automatically format code. Just run standard --fix and say goodbye to messy or inconsistent code.
• Catch style issues & programmer errors early. Save precious code review time by eliminating back-and-forth between reviewer & contributor..

A git hook was added to ensure that the conventions are respected.

The changes in this merge request were mostly done by the --fix option of the standard tool.
Some linter exceptions were added to ensure no logic change in this merge request. In the future these exceptions should be removed and the underlying issues should be fixed:

• Buffer.from should not be used anymore: Warning on Buffer(var) and new Buffer(var) standard/standard#693
• Errors were not handled in some cases
• Global variables: log, config ...
• callback(true) is not recommended: New Rule: no-callback-literal standard/standard#623

Other than that == was used instead of === and some variables were re-declared in the same scope.