better semantic for 'opam switch'

[samoht]

The current semantics of opam switch is not very clear.

A possible improvement could be:

$ opam switch -add jane-elisp -alias-of 4.00.0
$ opam switch -add 4.00.0 # here -alias-of 4.00.0 is implicit as alias and compiler have the same name)
$ opam switch jane-elisp
$ opam switch -rm jane-elisp

[samoht]

Incidentally, there is currently no way to remove an alias, so this new design fix that.

[cagdasbozman]

Another possible improvement:

$ opam switch -install {compiler}           //to install
$ opam switch [-clone] -install {compiler}  //to install [and try to keep installed packages] 
$ opam switch -remove {compiler}            //to remove a compiler
$ opam switch -reinstall {compiler}         //to reinstall a compiler
$ opam switch {compiler}                    //to switch
$ opam switch -list                         //to list all available compilers 

[tuong]

Notes :

• we can rename opam switch to opam ocaml or opam compiler...
• for @lefessan : If we want to work with two different OCaml at the same time in two terminal, we could propose :
  opam --ocaml alias1 <subcommand>,
  opam --ocaml alias2 <subcommand>.
  The locking will then move under .opam/alias instead of the current .opam.

[samoht]

I quite like @Cago proposition (and I would prefer keeping opam switch). @tuong, good idea, opam --alias <foo> <subcommand> could also help fixing #66.

[samoht]

Moving to 0.6 as the feature is already working fine in 0.5 - just need some more though to find the proper design.