Add categories to Cargo.toml

[shepmaster]

Hi! crates.io now supports categories, which are a curated list
of topics aimed at helping an end-user coming to crates.io looking for
"a crate to do ______".

We're sending pull requests to selected crates to add categories in order to help
populate the categories and seed their usefulness. We've made a guess at the best
category/categories for this crate; if it doesn't fit, please feel free to take
a look at all the available categories and their descriptions and
the slug values that should be specified in your Cargo.toml and pick
different ones. If you have a category in mind that isn't available, you can
send a PR to this file on crates.io to propose additional
categories.

Crates can have up to 5 categories, and uploading categories to crates.io
currently requires publishing a new version with a cargo nightly from 2017-01-18
or later (it needs to contain this PR).

We've published a blog post with further details about categories.
The blog post also talks about the new crates.io support for CI badges, which
you may be interested in adding as well.

Please let me know if you have any questions!

[shepmaster]

Additionally, it looks like your TOML was malformed (missing a comma) and the multiple license format is supposed to use a slash:

This is a string description of the license for this package. Currently
crates.io will validate the license provided against a whitelist of known
license identifiers from http://spdx.org/licenses/. Multiple licenses can be
separated with a /.

I hope I didn't overstep my bounds!

[LeopoldArkham]

Not at all! Had the comma fixed locally and on crates, but the slash for licenses was news to me.
Thanks for this, I'll publish in a bit.