Add scalding-cats module for cats typeclasses on scalding types

[johnynek]

We keep implementing local instances of these. This gives the most useful instances for scalding types.

The Execution instances are particularly useful.

@ttim @dieu please take a look.

[dieu]

@johnynek could you add some tests code with examples how it will useful for us or more details in description what we will benefit?

Thanks.

[johnynek]

@dieu please take a look at the tests.

I think giving a how-to is out of scope here. This is for users that wish to interop Execution (and to a much smaller degree TypedPipe) with cats and cats-effect. You might take a look at:

https://typelevel.org/cats-effect/datatypes/io.html

By implementing Effect for Execution, we can interop with many nice IO related methods.

Note, these tests uncovered a bug in the testing framework I reported here: typelevel/cats-effect#441

[johnynek]

@ianoc can you take a look at this if you have any free time?

I was able to make a change to pass the laws without weakening the gens.

[ianoc]

lgtm when green, the cats tests i would think are pretty complete and nice to be able to hook into a lot of them here

[dieu]

@dieu please take a look at the tests.

I think giving a how-to is out of scope here. This is for users that wish to interop Execution (and to a much smaller degree TypedPipe) with cats and cats-effect. You might take a look at:

https://typelevel.org/cats-effect/datatypes/io.html

By implementing Effect for Execution, we can interop with many nice IO related methods.

Note, these tests uncovered a bug in the testing framework I reported here: typelevel/cats-effect#441

thanks for tests.

[johnynek]

whoops... travis was not actually running the tests...

[ianoc]

Ha woops !