Add env var to control stripping debug info

[musicinmybrain]

Before this commit, debug info is stripped unconditionally on Linux.

This commit adds an environment variable UJSON_BUILD_NO_STRIP that disables this behavior. This is helpful for distribution packagers who would otherwise have to patch setup.py to prevent stripping.

Fixes #506

Changes proposed in this pull request:

• When environment variable UJSON_BUILD_NO_STRIP is set to 1 or True, do not strip debug symbols from the compiled extension. When it is unset, or set to any other value, maintain the previous behavior of stripping them if the platform is Linux.

[bwoodsend]

Thanks @musicinmybrain!

[hugovk]

@bwoodsend I should document this somewhere (perhaps in RELEASING.md?):

Let's always add one of the Changelog: x labels to PRs, such as Changelog: Added for this.

Then the Release Drafter action will create/update the next release notes draft, and put the PR title in the appropriate section. It also takes care of the next SemVer number!

Please can you check you can see the current 5.2.0 draft at https://github.com/ultrajson/ultrajson/releases ?

[bwoodsend]

Oh that's how your changelog works. Yes I see it. I've added the label although it appears to have picked up this change anyway?

[hugovk]

Yep, when it ran earlier it just added this with no section header.

It runs when PRs are merged (but can also be triggered) and will overwrite the draft based on all the merged but unreleased PRs.

So the next time it runs it'll update the section.

Sometimes I'll edit PR titles before merge so they make nicer changeling entries. Just before release, the draft can be fine tuned if necessary, but usually it's not needed.