code: function isBetween(lower, upper) {
  	return function (val) {
  		return isNumber(val) && val > lower && val < upper;
  	}
  }
docs: Checks to see if a value is a negative number
  @param {number} lower - the lower boundary value to check against
  @param {number} upper - the upper boundary value to check against
  @returns {function} - a validator function
  @memberof vet.numbers