Binary distribution

[Armael]

The current workflow for installing Creusot it too complicated. Ideally we'd like cargo creusot setup to take care of everything, and avoid using opam on the side. For this we need:

• [ ] binary builds of alt-ergo. (Almost there, they exist but report the wrong --version: https://github.com/OCamlPro/alt-ergo/issues/1131 -> wait for release 2.6 to include the fix)
• [ ] binary builds of why3 (including why3 ide),
• [ ] make binary builds of creustot-rustc and cargo-creusot, and decide how we want to distribute them to the end users.
• [ ] figure out what we want to do on windows (the above items being for linux / macos)

[xldenis]

make binary builds of creustot-rustc and cargo-creusot, and decide how we want to distribute them to the end users.

As a note, this is probably the least critical on this list, rust developers intrinsically have cargo on their machines so cargo install should be good enough, especially at first.