Type and validity assertions

We currently have no assertions in the code of almost all projects. This often leads to longer debug times, because of messages like cannot read property length of undefined whereas with assertions we could have something like ValueX is not a Buffer.

This should at least be mandatory on public APIs, to ensure that the user is using the lib correctly. NodeJS does just that and so do many libraries.

This is a duplicate of scality/IronMan-S3#92, and many thanks to @adrienverge for his helpful input on this.

[adrienverge]

100% agree on this.

👍 this needs to be added in the common rules.

[koolfunky]

👍