Display some built-in anagrams while we read the dictionary, for fun
Move "bag" into its own package.

Not sure this is the right way to do it, but it compiles and runs ...
New func bag.FromBigInt; use it instead of exporting the field name
Rename WordToBag => FromString
bag.Subtract now returns a bool, not an error.
Un-export a couple of functions

Only the test uses 'em
Add a (currently-unused) "letters" field

... which someday may wind up holding the actual data, in lieu of the bigInt
Add bag.GobDecode
Keep the letters sorted.
Cut over from numbers to strings!