Adds the magic `frozen_string_literal: true` comment to every file and
enables a Rubocop rule to make sure that it's always going to be there
going forward as well.
See here for more background [1], but the basic idea is that unlike many
other languages, static strings in code are mutable by default. This has
since been acknowledged as not a particularly good idea, and the
intention is to rectify the mistake when Ruby 3 comes out, where all
string literals will be frozen. The `frozen_string_literal` magic
comment was introduced in Ruby 2.3 as a way of easing the transition,
and allows libraries and projects to freeze their literals in advance.
I don't think this is breaking in any way: it's possible that users
might've been pulling out one of are literals somehow and mutating it,
but that would probably not have been useful for anything and would
certainly not be recommended, so I'm quite comfortable pushing this
change through as a minor version.
As discussed in #641.
[1] https://stackoverflow.com/a/37799399
* Rename the `Update` operation to `Save`
* Add the `update` class method to all saveable resources
* Add tests for update method
* Add tests for plans, invoice items, and application fees
Usage on a top-level collection:
```
Stripe::Customer.list.auto_paging_each do |customer|
puts customer
end
```
Usage on a subcollection:
``` ruby
customer.invoices.auto_paging_each do |invoice|
puts invoice
end
```
We've also renamed `#all` to `#list` to prevent confusion ("all" implies
that all resources are being returned, and in Stripe's paginated API
this was not the case). An alias has been provided for backward API
compatibility.
Fixes#167.
Replaces #211 and #248.
