Create a branch for 0.6.x?

[realityking]

I read @mraleph's blog post about optimizing source-map parsing without WASM earlier this morning. Since 0.6.x will be used for a long time in the Node.js ecosystem.

I'd love to apply some of his lessons to the code base. Would you be open to creating a 0.6.x branch to send pull requests against and eventually releasing a 0.6.2?

[kurtextrem]

He also posted the following graphs:

[fitzgen]

As of #325, the Rust+Wasm is another 3x faster. See http://fitzgeraldnick.com/2018/02/26/speed-without-wizardry.html for details.

[realityking]

Hey @fitzgen, That's great - and I look forward to using it myself. But there are a lot of projects out there who will be relying on the 0.6 series for the next ~1 year until Node.js 6 is out of support. It would be great it those projects could benefit from the work already done by @mraleph.

I'm not at all advocating to abandon the WASM efforts, but the wider Node.js ecosystem is not ready to drop support for Node.js 6.

[7rulnik]

I ported optimizations from the article into https://github.com/7rulnik/source-map-js
This fork 400% faster in parsing and 30% faster in serializing than original 0.6 version