Upgrade Brotli to v0.5.2

[quittle]

This upgrades Brotli to v0.5, which is the latest available branch on GitHub.

[googlebot]

We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for the commit author(s). If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.

[anthrotype]

well, if anything, you want to checkout the submodule at the latest tagged release:
https://github.com/google/brotli/releases/latest
... which is not that branch you're pointing to, but is the tag 0.5.2, with hash 66c14517cf8afcc1a1649a7833ac789366eb0b51

[anthrotype]

oh, that's already the case!
sorry, I was misled by the PR title, I should have checked first 😬

[quittle]

CLA re-check

[googlebot]

CLAs look good, thanks!

[fred-wang]

Note that @khaledhosny has opened #61

[quittle]

I saw that but figured that it would be better to upgrade to a release commit instead of HEAD of master.

[quittle]

Is Google interested in taking this PR?

[rsheeter]

We be interested :) Thanks for the PR and sorry for the slow response.

However, could I impose on you to bump brotli to the current latest release (0.5.2)? - the commit in this PR doesn't appear to match any currently listed on https://github.com/google/brotli/releases.

[quittle]

This commit is actually 0.5.2. they are both tagged to the same commit ID. I can update the commit message if you like.

[quittle]

Okay, I've updated the commit message to reflect the more accurate version number

[quittle]

I have created a new PR for this change after adding tests and fixing build issues. I must have missed the conversion of Brotli to use a C interface instead of the C++ one it used when I converted this commit from one used for a personal project. See #65 for the new revision, which is a bit more invasive