Add cacheable config

[DanPurdy]

By default the config is now cached on each invocation of sass-lint with an option to override this behaviour.

You can override this behaviour if you want, an example would be someone tweaking their sass-lint config within a IDE plugin.

Updated the tests to work with this new implementation.

Some of the crude benchmarks I ran for loading the config when cached showed an average of a 26% speed increase loading each rule as opposed to always loading from scratch though i'm sure with tweaks we could improve this and definitely an opportunity with 2.0

Looking for feedback here about if everyone is happy for this to move forward. It follows our usual pattern of preference i.e. options > user config > defaults

closes #279

DCO 1.1 Signed-off-by: Dan Purdy <danjpurdy@gmail.com>

[DanPurdy]

Also closes #403

[DanPurdy]

Ready for review now

[benthemonkey]

A little bit off-topic, but do we need the devDependency on the deep-equal module? My understanding is that the reason to use it over assert.deepEqual is to return a boolean instead of throwing an error. However, we only use it in tests, where throwing is fine.

[benthemonkey]

Other than that, LGTM. Added a console.log to the cached config condition in config.js and verified that the branch is being hit instead of loading the config again.

[DanPurdy]

Thanks @benthemonkey, I've tried to cover every eventuality with the tests and they're actually doing something now so good catch there! @bgriffith and @Snugug should probably look this over before we merge it as it's quite far reaching in what it does.

As for deep equal, correct me if i'm wrong but we'd need to use the assert.deepStrictEqual method which I 'believe' isn't supported in earlier versions of Node that we test against still? I don't mind removing if we need to though.

[benthemonkey]

Oops, you're right, 0.10.x doesn't support assert.deepStrictEqual.

[Snugug]

In general I like this rule. Think it should be off by default as it's one of those things that can potentially be a gotcha bug that's hard to track down.

[DanPurdy]

Ok, i'll update this so it isn't enabled by default then, I think that does make sense.

[DanPurdy]

Ok updated the defaults to false now. Ready for final review.

[benthemonkey]

This LGTM

[DanPurdy]

Feel free to merge it, I just wanted the other guys to give it a once over before we merged it in the first place. All good now though.

[bgriffith]

Funky indentation?

[DanPurdy]

Turns out the indentation was fine @bgriffith, though it looks wrong to me!

[bgriffith]

Sorry about that!