Add evict function for ARC

[jasonsurratt]

Adds evict functionality to the ARC cache. See also #22

[hainesc]

@jasonsurratt Awesome work!

Before I create a PR, I see this one, it is almost the same with mine.

Looking forward this PR get merged as I need onEvict callback function in one of my project. I add support of onEvict callback in my fork repo.

[hainesc]

@jasonsurratt, Please know that you need to sign the CLA.

[jasonsurratt]

@hainesc Thanks! I signed the CLA.

[immesys]

I would really like this functionality. Any chance it can be merged soon?

[jasonsurratt]

Please let me know if there is anything else I can do to get this merged. I don't have write access and it has been dangling out here a while. Thanks!

[hashicorp-cla]

All committers have signed the CLA.

[jackedelic]

Could we get this merged :) ? Need this feature to make my boss happy

[jasonsurratt]

This ceased to be relevant to me about 3.5 years ago so I'll let it die. Looks like the conflicts are pretty minor but I haven't used go in so long I'm afraid I may make a silly error merging them.