Add labels! and labels_sep_by! utility macros.

[dashed]

Closes #7

I use suggestion from #7 (comment)

---

I added labels_sep_by! because I wanted to be able to customize delimiters. I use it to generate the style attribute of the element.

---

@Stebalien I couldn't get this to work labels!("active" if false) since:

expr and stmt variables may only be followed by one of: => , ;

according to https://doc.rust-lang.org/book/macros.html

Any suggestions?

[dashed]

I realized I forgot to create a branch. 😓

[Stebalien]

Nice!

expr and stmt variables may only be followed by one of: => , ;

according to https://doc.rust-lang.org/book/macros.html

Any suggestions?

😢 I was thinking of patterns. Oh well. => is clear enough.

[Stebalien]

Instead of importing and calling, just use the fully qualified syntax: $crate::RenderOnce::render(&$item, tmpl)

Otherwise, you run the risk of running into conflicting functions.

[Stebalien]

Just a few nits and this looks good to go.

[dashed]

I amended with documentation and suggested refactor.

I also refactored the macros to add separator only if there is a previous label. This was an edge case I missed.

[Stebalien]

Why mark this norun?

[dashed]

I copied the doc comments from another macro and reworked it. I wasn't sure what norun does. I can remove it if you like.

[Stebalien]

That's because I've been lazy 😴. I just pushed a commit that removes the norun directives (so you can see how to do this). (...I also ended up having to fix many of the examples which is why norun should be avoided...).

[dashed]

I refactored and I reworked the docs a bit; hope it's less awkward :)

[dashed]

Removing norun breaks travis.

[Stebalien]

See the updated docs (where I've removed norun). Basically, you have to wrap your example:

# #[macro_use]
# extern crate horrorshow;
# fn main() {
call_macro! {
}
# }

The # prefix means "don't display this line".

[Stebalien]

The new docs are great! Much better than I would have written, I hate writing docs... I'll merge after you fix the travis failure.

[dashed]

I fixed the doctests and squashed the commits.

---

I think we ironed out all the issues for this PR.
@Stebalien , thanks for the assistance in this PR! 👍

[Stebalien]

Thank you! It was a pleasure working with you.