function plot( x, y ) {
		if ( arguments.length === 2 ) {
			return new Plot( x, y, opts );
		}
		return new Plot( opts );
	}
Creates a plot.

@private
@param {Array} [x] - x-values
@param {Array} [y] - y-values
@throws {TypeError} must provide valid options
@returns {Plot} plot instance