readme: improve compression example

wsflate: avoid double buffering when using flate.Reader (gobwas#137)

This commit makes wsflate.suffixedReader to optionally implement
io.ByteReader. That is, if source object is buffered (bytes.Reader,
bufio.Reader etc.) and implements io.ByteReader, but suffixedReader not,
then flate.NewReader() will allocate new bufio.Reader for it. This
commit fixes it and adds runtime checks on suffixedReader source to hide
ReadByte() method if source is a pure io.Reader.

Fixes gobwas#130

spell fix

wsflate: IsCompressed() shortcut

wsflate: fix no new variables typo

github: autobahn report as artifact

github: fix build on newer Alpine Linux for tests

autobahn/docker: fix building image

fix for checkptr (gobwas#102)

* fix for checkptr
* remove unsafe methods

Fixes: gobwas#99

minor fixes on documentation. (gobwas#82)