levels: Ability to use objects in `getTechs` values

[veged]

Right now we write some thing like that:

exports.getTechs = function() {
    return {
        'bemjson.js' : join(PRJ_TECHS, 'bemjson.js.js'),
    };
};

It will be useful if we can write some thing like this:

exports.getTechs = function() {
    return {
        'bemjson.js' : getMyCustomTechModule()
    };
};

So we can implement tech modules inline, without need to create file.

[narqo]

:+1:

[scf2k]

@veged, @narqo, @arikon take a look https://github.com/bem/bem-tools/pull/446