failing test case
hex & unhex but test failing on "illega UTF-16 surrogate"
overriding data_coding:8 as utf-8
decode utf8 before string comparison
coding directive no longer needed
make hex encode & decode part of multipart saving & loading functions (thanks @hodgestar)
Merge branch 'feature/issue-646-smpp-crash-on-multipart-ucs2-delivery-sm' into develop