update unicode/utf16
 add Decode.md
 add DecodeRune.md
 add Encode.md
 add EncodeRune.md
 add IsSurrogate.md

Signed-off-by: sndnvaps <sndnvaps@gmail.com>
Update IsSurrogate.md
Update IsSurrogate.md
Merge pull request #189 from sndnvaps/master

Update Unicode/utf16 package