Build and link to tcmalloc statically

[brson]

This makes gperftools a submodule, adds a tcmalloc-sys crate, and builds and links to tcmalloc.

If somebody really wants to use a local tcmalloc they can enable the no-build feature.

Note that I've only tested on x86_64-linux-unknown-gnu, and so I whitelisted that target in the build script — for any other target the script will fail.

This also bumps the version number. If you accept this PR I hope you will publish a new revision.

[jmcomets]

Thanks for the PR! I do have a few minor review notes on the build.rs script.

Aside from the code itself, I'm wondering if a submodule is the right way to go here. For example, tensorflow-sys clones the repository and checks out the specific tag before building from there. If you have any extra info on that, I'd be interested, but I'll accept it anyways.

[brson]

@jmcomets Re submodule vs cloning during build, I am mostly copying from jemallocator here. The main reason to use a submodule and not do a clone that I can think of is that git clone only works for branches and tags, not arbitrary commits. But gperftools is well tagged so that doesn't really apply. I will change it to do a clone.

[brson]

Thanks for the review.

I pushed a rebase that addresses all comments.

I deleted info! in favor of println!. "bundled" is now not the default, and the tcmalloc-sys crate isn't used when not "bundled".

I also removed the version bump. Since this is adding an optional feature I don't think a major bump is necessary. You can handle the versions.

[jmcomets]

This looks great and works out of the box, well done. :+1:

[jmcomets]

FYI there may be some notification spam here while I get this published to crates.io, don't mind it too much