[MNY-24]: Language localized formatted string

[danthorpe]

Representing MoneyType in a suitable locale.

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[danthorpe]

This PR adds functionality to get a formatted string for MoneyType using an arbitrary locale identifier. This makes it possible to have say USD money, but get a localized description for a Spanish speaking country for example.

let dollars: USD = 99

// Will use the current locale of the user
print("You have \(dollars)")

// Will use the locale for a Spanish speaking Spaniad
let formatted = dollars.formattedForLocaleId("es_ES")
print("She has \(formatted)")

For an user with English language, in the United Kingdom (en_GB), this will print out:

You have US$99.00 She has 99,00 US$

Changing the device to Spanish language in Spain region (es_ES), it will print out:

You have 99,00 US$ She has 99,00 US$

The problem with this, is that it's a little unsafe to use strings. So, I've added a Locale type. This is an enum and provides type safety and type completion. You can use it like this...

// Will use the locale for a Spanish speaking Spaniard
let formatted = dollars.formattedForLocale(.Spanish(.Spain))
print("She has \(formatted)")

For a device in English language in United Kingdom region (en_GB), it will print out the same as before:

You have US$99.00 She has 99,00 US$

For a device in German language in Switzerland region (de_CH), it will print out:

You have US$ 99.00 She has 99,00 US$

Notice how the en_GB formatted string does not have a space between the $ sign and the first digit, but the de_CH does. The es_ES places the symbol after the digits. And the grouping and decimal strings are different.

Now, I think in most use cases, this is totally unnecessary, as in the vast majority of time you want to display values using the user's current language and region settings. But on the other hand, I think being able to explicitly state what locale you want to use is pretty neat.

Note also, that I am a Brit living in London, and this framework is written in English (en_GB) however, the type names for the Locale (and the nested countries) are generated from the en_US locale.

Anyone got any thoughts on this? /cc @mrdavey.

[danthorpe]

Fixes #24

[mrdavey]

This is great @danthorpe . Very flexible and covers all the use cases I have come up with :+1:

[danthorpe]

@mrdavey okay, great. in which case, I'll close #24.

I'm just sorting out some documentation issues, and then I'll release 1.4.0 which will include these changes.