TranscodingStreams.jl 0.4

• Implement Base.readavailable (#12).
• Test CodecBase.jl (#15).
• Add expectedsize and minoutsize methods (#14).
• Prohibit stream from changing read/write mode (#17).
• Add unread and unsafe_unread (#13).
• Rename state to mode (#19).
• Deprecate Identity and IdentityStream (#20).
• Add transcode(::Type{Codec}, data) method (#23).
• Implement shared buffers (#22).
• Add seek operations to NoopStream (#26).
• Add Base.position to NoopStream (#27).
• Implement stop-on-end stream (#25).
• Implement Base.seekstart and Base.seekend (#28).
• Add stats (#30).
• Change mode from idle to read when eof is called (#31).
• Fix loading on 0.7 and reenable testing (without coverage) (#33).
• Bump requirements (#36).