devel/ocaml-cmdliner: prepare for OCaml 4.06+

• Update to version 1.0.4, now licensed under ISCL
• Set LICENSE_FILE as it is not just a boilerplate but contains actual copyright information
• Drop dependency on `devel/ocaml-ocamlbuild' (unused since v1.0.3)
• Don't hand-roll build and installation routines, use provided
• Convert to static pkg-plist and install documentation files
• Mark as parallel build unsafe for the moment due to this error:
  
  File "cmdliner.ml", line 1: Error: Corrupted compilation unit description
  
  or this:
  
  File "cmdliner.ml", line 1: Error: The files cmdliner_arg.cmi and cmdliner_term.cmi make inconsistent assumptions over interface Cmdliner_term