🎁 Add SassDoc grammar patterns

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Description of the Change

Adds grammar patterns for highlighting SassDoc comments, similar to how JSDoc blocks are handled in language-javascript.

Benefits

Having docblocks highlighted makes them easier to read, and can encourage their use.

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I think the patterns for this should be pretty good now. I'm not super-familiar with using Jasmine for tests though — is there an easy way to run the tests locally?

EDIT: Looks like atom --test spec should work; if there's a different workflow for local testing let me know!

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Tests are added! This should be good to go, barring any review feedback or concerns. 🙌

[lee-dohm]

@stormwarning Would it be possible for you to give us a "representative" before and after screenshot just so that I can get an idea of what changes this is going to make? Our normal language person is out right now and I'm filling in a bit.

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@lee-dohm Absolutely, thanks!

Before:

After:

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Realised @type tags don't need {} around the type name so I fixed that up. Is there anything else I can do to help move this forward?

[lee-dohm]

Looks good to me! Thanks for the help 🙇