- no more version.sh, use config.ml.in and version.tex.in instead
- dynlink compatibility is moved to config.ml
- comment out unused sections in Makefile
- provide the explicit --enable-ide option
- provide the explicit --enable-plugins option
- require at least Ocaml 3.10
- remove *-yes and *-no targets from Makefile,
  use ifeq() instead

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default actions in case explicit options are missing.

The command line has the following structure:
    
    why [options] [[file|-] [-t <theory> [-g <goal>]...]...]...

Summary:
    
    Qualified theories come from the library, not from file.
    When the driver is not specified, pretty-print theories.
    When neither --prove nor --output are given, print tasks.
    When no theory is specified for a file, use every theory.
    When no goal is specified for a theory, use every goal.

Examples:

    % why.opt
    [shows usage information]

    % why.opt test.why
    [prints the contents of test.why]

    % why.opt -t int.Int
    [prints the library theory int.Int]

    % why.opt -D drivers/z3.drv test.why
    [sends every task from test.why to stdout]

    % why.opt -D drivers/z3.drv -o directory test.why
    [creates ./directory/ if it's does not exist and
     sends every task to a separate file in ./directory/]

    % why.opt -D drivers/z3.drv --prove test.why -t ThA
    [calls the prover for every goal from theory ThA in test.why]

    % why.opt -D drivers/z3.drv --prove test.why -t ThA -g G1 -g G2
    [calls the prover for G1 and G2 from theory ThA in test.why]

    % why.opt -D drivers/z3.drv -t int.Abs -g G1 test.why -t ThA
    [prints G1 from int.Abs and every goal from ThA in test.why]

  move this implementation to eliminate_let.
- initial commit of eliminate_definition : the goal is
  to translate definitions by match into series of axioms.