6.1.0 Compatibility

Continuing from the discussion at https://github.com/RubyMoney/money/issues/354 I upgraded Money to 6.1.0.

That stopped the deprecation notices and broke compatibility with Monetize. Monetize expects Money to respond to `assume_from_symbol`. `Money.assume_from_symbol` was removed in 6.1.0. Monetize relied on this behaviour to determine if the currency should be assumed by the passed symbol.

This patch restores that behaviour by adding `Monetize.assume_from_symbol`. It defaults to `false` as it did in Money.

Reading through the history it feels like this project is moving away from making these sort of assumptions (Assuming $ to be USD is very one-sided). In the interest of making the 6.1.0 upgrade as smooth as possible I suggest keeping this behaviour initially and then deprecating it in a future release.

Personally, I don't care for this method. I just want to use 6.1.0 without deprecation notices. I welcome any feedback you have to get this patch merged.

Cheers,
Tate