function BuildManager (args, doc) {
    this.steps = [];
    this.args = args;
    this.doc = doc;
    this.ended = false;

    var that = this;
    this.on('step', function (pkg, name) {
        setImmediate(function () {
            that.run();
        });
    });
    this.on('error', function (err) {
        that.end();
    });
}
Constructor for BuildManager Objects, used to run a build process built from
steps including before and after rules.

@constructor