Added support to use key identifier in the key codes array

Key codes represent the location of a key on the keyboard. Relying on that too much for characters like comma will make this plugin absolutely unusable in i18n environments (comma is located on a different physical key).

Entering key identifiers.. Unique for each character (Comma is 'U+002C', see: http://codepoints.net/U+002C). Using those would be better for any i18n use case).

This one line addition adds support for those.