v1.7.0 - Enhanced Character Encoding Support

Change summary:

[#25, #26] Add getStandard method to EDIStreamWriter
[#33. #34] Decode input characters and encode output using provided Charset name

Note: Developers using EDIStreamWriter must be aware that the method of output encoding introduced in #34 utilizes a buffer and a call to flush() or close() is critical after writing all segments and elements. An explicit flush is not necessary when endInterchange() is used.