Perl: Implement protocol_version option in encoder

This means that we do not have to play silly games like introducing
a separate option per protocol version in the future. Sorry, this is
how this should have worked from the start. My bad.
Perl: Protocol v3 (as a no-op) in decoder

Also introduces some defines in srl_protocol.h that will be used
shortly.
Necessary version bumps
Perl: Expose high-bit-set magic variant
Perl: Actually emit and consume high-bit magic

Includes tests for detecting accidental UTF-8 upgrades.
Spec: Describe v3 spec change wrt. magic string
Perl: Check in copy of miniz
Perl: TODO notes about configure work for miniz performance
Spec: Add zlib compression doc type
Perl: Add ZLIB doc type to protocol header
Perl: Remove dead code
Perl: 1st attempt to add zlib support to decoder
Perl: Tentative zlib support in hobodecoder
Perl: First stab at zlib compression in encoder
Perl: Duh. Remove truism from if()
Perl: Further zlib support in encoder
Perl: zlib/encoder fixes
Perl: zlib/decoder fixes
hobodecoder and zlib
Perl: Run some v3 && zlib tests