code: function hasMethod (signature) {
      // convert signature string to method and function name
      signature = getValidSignature(signature)
      // get module
      var module = immutable.modules[signature.moduleName]
      // return false if module does not exist
      if (!defined(module)) {
          return false
      }
      // check if method exists
      return defined(module[signature.methodName]) ? true : false
  }
docs: @function hasMethod
  
  check if method exists.
  
  throws error on invalid method signature.
  
  @param {string} signature - ModuleName.methodName of method
  
  @returns {boolean}
  
  @throws {Error}