Splitting TXT and SPF records longer than 255 chars into more strings

- DNS defines that a single string can be of max length 255 chars
- However, there can be more of then
- So, if the tota lstring length is longer, it's split into more strings
Fixed SPF record to ba handled the same way as TXT record

- strings are quoted
Fixed checking the TXT/SPF record value size

- Record size can be bigger than 255 characters but in that
  case it needs to be split into more smaller parts
  e.g., "a" "b" "c" instead of "a b c"
- The old implementation expected the value size to be max 255
  in total, which was wrong
New changes file entry and new version
Added URL tah to spec file
Merge pull request #29 from kobliha/splitting_txt_spf_records

Splitting TXT and SPF records longer than 255 chars into more strings