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Earlier we anticipated declaring projections in this way,
but never implemented it, and I still think this would
be a hack, not in line with the rest of the language.
Anyway, it's a three-line change, easily revertible.

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]

It's not more expressive but much nicer than epsilon.