Fix content length for non ASCII (e.g. UTF8)

The Content-Length header should indicate the length in number of bytes not in number of characters. 
String.length is replaced by Buffer.byteLength(String)
Merge branch 'patch-1' of https://github.com/bachwehbi/iodocs into bachwehbi-patch-1
Merge branch 'bachwehbi-patch-1'