Remove deprecation notice and raise error when strings cannot be parsed by bigdecimal

[TayKangSheng]

issue: #307

Why

Currently we attempt to parse strings with BigDecimal, and we default to BigDecimal(0) for cases where the string cannot be parsed. In v3, we want to remove this fallback and we recommend users to parse the money first before using initializing a new money object.

What

This is a breaking change

We now raise ArgumentError if the provided value is a string and cannot be parsed by BigDecimal.

Money.new("$1.00", "USD") # -> raises invalid value for BigDecimal(): "$1.00" (ArgumentError)

[elfassy]

last event in the logs was 4 weeks ago, we're good to merge this in v3!