Move piqi-camlp4 into piqilib and separate piqilib and piqirun
Decouple piqilib and piqirun; move piqirun_ext.ml from piqilib to piqirun

- piqilib no longer depends on piqirun
- piqirun_ext becomes a part of piqirun
- piqirun becomes a package with two subpackages: piqirun.pb -- for Protobuf
  serialization and piqirun.ext -- for multi-format serialization
(ocaml) update examples and tests to use the new runtime package names

The packages where renamed as follows:

piqi.runtime -> piqirun.pb
piqi.lib -> piqirun.ext
Adjust "make ocaml-install" to follow the new OCaml libraries layout
Move several symlinked definition files to piqi-tools/
piqi-tools build is no longer depends on piqic-ocaml

We achieved this by pre-generating and piqi-tools/_piqi.ml from .piqi and making
them a part of source distribution.

To update the generated _piqi.ml files, call "make reboot" in piqi-tools.
Improve piqilib reboot procedure (make reboot)
Remove tests/boot_proto2piqi -- it wasn't really testing anything

... just some legacy code
Edit comments
Build improvement: don't install ocaml libraries as a part of the build

With all the recent changes, symlink is sufficient
Optimize build: don't build ocaml stuff by default

Essentially, this excludes piqirun-ocaml and piqic-ocaml.
Deprecate "piqi version"; use "piqi --version" instead
Better division of interfaces between piqilib and piqi-tools

The ultimate goal is to make piqilib interfaces more stable so that we can
detach piqic-ocaml and piqirun-ocaml and move them into a separate repo.
More interface separation in the OCaml-specific parts
piqi: minor change in the usage string formatting
Add piqic-ocaml --version and --piqi-version flags

They are used for printing piqi-ocaml and piqi versions respectively.
Fix false "unknown field" warnings produced by "piqi compile"

It was printing warnings even though fields were properly declared as custom
fields via the custom-field property.
Small interface improvement in piqi_command.ml
Minor build change

Rename META.tmpl to META.in
build: rename "make reboot" to "make piqi" and add a top-level "make piqi" rule