This allows the crate to build with Rust older than 1.62.

Use explicit Default for GzHeaderState enum.

This resets the minimal required rust version to 1.53.

Fixes #220

Fix spare capacity handling

- fix wrong docs of `bufread::GzDecoder`, `bufread::GzEncoder`, `bufread::MultiGzDecoder`
- make the types of inner reader and exported trait explicit.
- explicit state the pull model: user initialize the read, then data is
  read from the underlying stream.

Fix and unify docs of `bufread` and `read` types.

Reset StreamWrapper after calling mz_inflate / mz_deflate

prepare next patch-release