v1.13.0

Changelog

b4546d4 Add gzip HTTP handler/client wrapper (#383)
b7e9e8e Make content detection ignoring write sizes.
6315923 gzhttp: Don't compress HEAD requests (#387)
f51c216 gzhttp: Reduce allocs more (#385)
3e13b83 gzhttp: Support Flush always (#386)
ab9d76f s2: Clarify EncodeBuffer usage (#384)
d172db7 zstd: Detect short invalid signatures (#382)
e95c300 zstd: Spawn decoder goroutine only if needed. (#380)