Update README with unsupported currencies and exchanges

[antstorm]

I did a bit of testing around Google Finance Converter and found out that not only it doesn't support all the currencies that money gem has, but it also has a list of exchanges that it can not perform.

Here's a script that I used:

require 'money'
require 'money/bank/google_currency'

Money.default_bank = Money::Bank::GoogleCurrency.new

rate_error = {}

Money::Currency.stringified_keys.each do |from|
  Money::Currency.stringified_keys.each do |to|
    begin
      Money.new(100_00, from).exchange_to(to)
    rescue Money::Bank::UnknownRate
      rate_error[from] ||= []
      rate_error[from] << to
    rescue StandardError
      p "Unsupported currency: #{from} or #{to}"
    end
  end
end

Also, since every exchange rate is fetched one by one, the whole process took quite a bit of time and ate 144MB (!!!) of traffic. Which makes me think that we need to deprecate this gem in favour of something better.

[printercu]

👍 For 31684 (178 \ 2) conversions its just 4kb for each rate. Don't think it's too much, while every app don't need them all in a single moment.

However it'll be good to find other free api.

[antstorm]

Yeah, you're right, most of the apps won't need all the rates, but I'm pretty sure that the entire exchange ledger should be no bigger than 500KB.

Anyways, googling for a swappable API didn't give much results, so I wonder if there's a reason for not deprecating this repo in favour of other better APIs out there (like EU central bank or currencylayer).

[printercu]

When I tried that gems, they had more missing rates than googlecurrency (about a year ago).

[antstorm]

Oh, really? So you think that alternatives are not good enough and there's room for another one?

[printercu]

At least we may not deprecate googlecurrency while it works. I'll check missing rates in eucb later.

[antstorm]

Yeah, sure, makes perfect sense to keep it running then