Utility handling (un)installation of Opam .install files

 opam-installer is a small utility, part of Opam, that can interpret
 Opam's .install files and take the appropriate actions.
 .
 OPAM stands for OCaml PAckage Manager. It aims to suit to a vast number
 of users and use cases, and has unique features:
  * Powerful handling of dependencies: versions constraints, optional
    dependencies, conflicts, etc.
  * Multiple repositories backends: HTTP, rsync, git
  * Ease to create packages and repositories
  * Ability to switch between different compiler versions