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- piqic was superseded by piqic-ocaml
- piqicc was superseded by the new bootstrap procedure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)