Rewrite of piqic-ocaml on top of "piqi compile" (work in progress)
More work on piqic-ocaml (work in progress)
More work on piqic-ocaml: finally, it generates piqi_piqi.ml for itself
piqic-ocaml can now generate code for piqilib (compiler-complier mode)
New build and bootstrap procedures that don't rely on old piqicc and piqic

The build is a lot simpler and faster now
piqic-ocaml: add generation of multi-format serializers
piqic-ocaml: fix generation of incorrect code for custom ocaml types
Update ocaml examples and tests to use piqic-ocaml instead of "piqic ocaml"
Remove piqic and piqicc and their references

- piqic was superseded by piqic-ocaml
- piqicc was superseded by the new bootstrap procedure
piqic-ocaml: edit comments
Move common piqi compile functionality to piqilib

It is used by piqic-ocaml and "piqi compile"
piqic-ocaml: add deprecation warning for the --gen-defaults flag
piqic-ocaml: fix compilation warning (duplicate piqi_piqi.cmi interface)
piqic-ocaml: add a new --ext flag (same meaning as --multi-format)
doc: update docs to reflect the change from "piqic ocaml" to piqic-ocaml
Update INSTALL.ocaml
piqic-ocaml: various code improvements