Let user choose compression algorithm

[emilk]

We currently use zstd to compress the profile stream. However, it compiles and runs very slow (see #130).

A great alternative would be lz4_flex, which both compiles and runs very fast. It is also pure Rust, so it works on Wasm.

I think it would be worth to refactor puffin to support multiple compression schemes/libraries (zstd and lz4_flex, initially). The compression scheme would need to be encoded in the data stream. The puffin_viewer binary would support all of them for maximal compatibility, but we would let users of puffin to opt-in to different compression libraries so the users can chose between fast compression and compilation, or high compression ratio.

Alternatively, if that is too much work, we can just switch out zstd for lz4 and have a big breaking change.

[repi]

agreed, zstd is a pretty big C dependency to bring in to clients as well. a smaller pure rust one would be nicer, and we don't need the highest compression ratios

[repi]

this is implemented