Add support for user-provided route tags.

[danxmoran]

Fixes #314.

I went with @@ for the syntax to get things rolling, but I'm not tied to it. I plan to have a follow-up PR that adds alphanumeric aliases for it and the other existing methods as part of #315.

[zarthross]

My initial thoughts are
1.) It would be nice to be able to do a single tag easily as well. (tag @@ route rather than List(tag) @@ route )
2.) Have some examples put into the rho-examples project

[zarthross]

I'll think on the symbolic operator as well. I have some time tomorrow night, I'll give this a good review then. Thanks for the PR!

[zarthross]

Looks good to me. I think the @@ has grown on me, since shapeless uses @@ for type tags. (I don't think it conflicts because its a type in shapeless and a method here)

My only complaint is the issue with precedence "tag" @@ ("foo" ** GET / "bar") it would be nice to be able to drop the parans for either order of tags vs desc.

[zarthross]

@danxmoran If you good with the current PR I'll happily merge it in.

[danxmoran]

Agreed that the mismatched operator precedence is annoying, but I'm ok with having it merged as-is 👍 thanks for the review!

[danxmoran]

@zarthross sorry to bother, is there anything else I can do to help get this merged?

[zarthross]

@danxmoran I was waiting for some other maintainers to comment, but seeing how no one has... i'll just merge it anyways. It'll get released with our next milestone.