Character Encoding in MSH-18 is ignored

[Stratus3D]

Other than defining MSH-18 as charset MSH-18 ignored (https://github.com/ruby-hl7/ruby-hl7/blob/master/lib/segments/msh.rb#L23).

From what I understand MSH-18 should contain the character encoding for all the segments after the MSH segment in the message. Most systems just use ASCII and leave this field blank, so it isn't a problem most of the time. It would be nice if the library checked this field and then handled the message encoding in accordance with the HL7 standard.