Log Message:
tex-tikzsymbols{,-doc}: update to 4.12a

New symbols: \Heart, \dHeart and \Maskey

New commands to define your own tikzsymbol:
  - \tikzsymbolsdefinesymbol for symbol definition.
  - \tikzsymbolsprovideandusesavebox to store and reuse symbols.
  - plus a few other public functions.