[PATCH] rewritten gsm 7 bit encoding

Hi, I've rewritten the GSM 7 bit default encoding as the current implementation results in wrong encoding for certain characters, e.g. '@'. The septet packing lacked the lookup and this only worked for characters that had a 1-1 mapping between their ascii value and the default alphabet table. I introduced a lookup table and now do the character translation before packing the data. Patch is attached.

I guess the decoding needs to be rewritten as well and I may provide a patch for that in the future as well. For now the encoding produced enough headaches for me :)

I adjusted the copyright stanza in these files but I'm not completely sure if this is appropriate or not, so feel free to remove, I won't be offended :)

Cheers Nico