Use ARGV_t instead of stringbuf in changelog parsing

Use ARGV_t instead of stringbuf in changelog parsing
- addChangelog() is a bad boy and modifies the string it grabs
  from getStringBuf(), be clean about it and grab a copy through
  argvJoin() instead
- addChangelog() would be better off walking and parsing over the
  argv directly instead of a joined string of it all, but leaving
  that exercise for some other rainy day