A rewrite in typescript.

[tinnick]

I rewrote the source in typescript. Please check and see if there are any problems in the code.

Deprecated module "sys" is replace with "util".

I could not find a way to implement:

levels.forEach(level => {
    this.prototype[level] = function() {
        ... // more code here
    }
})

in typescript so I used Object.assign in the constrcutor.