Update multiple formatter interface

[sferik]

I left a comment on #158 but I thought I would open an issue proposing a new interface for specifying multiple formatters:

SimpleCov.formatters = [
  SimpleCov::Formatter::HTMLFormatter,
  SimpleCov::Formatter::CSVFormatter,
]

This is the current interface:

SimpleCov.formatter = SimpleCov::Formatter::MultiFormatter[
  SimpleCov::Formatter::HTMLFormatter,
  SimpleCov::Formatter::CSVFormatter,
]

I think my proposal is better than the current interface because (conventionally) the [] method is used to fetch a value, not to set a value.

This proposal would not require breaking the current interface SimpleCov.formatter because the new method is named SimpleCov.formatters (with an “s”).

[fables-tales]

👍. Square brackets on constants doing things other than getting values are almost always a smell.

[bf4]

Sounds good to me. Would you mind submitting a PR?

[sferik]

Submitted.