Add support for lzma compressed tarballs

We've been playing around with using lzma for [CocoaPods.app](https://github.com/CocoaPods/CocoaPods.app), we're seeing over half the size of gzip with lzma.

| Type | Size (MB) |
| ------- |:-----:|
| Uncompressed | 107.9 |
| gzip | 32 |
| lzma | **14.5** |

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