Provide tools to programmatically create and maintain a build system,
and a library of small scripts to create a single file from its dependencies.
Get rid of hand-written build descriptions (e.g. make files).

Expose information the build tool uses to make decisions, so it is not
hidden by or specific only to credo.

Print executable commands as output.  For example, do scripts print
the primary commands they use to compile a target.  As another
example, credo with no targets runs lsdo, to list targets available in
the current directory, in the form of credo commands which may be
highlighted and executed in Acme.  Similarly, dodep with no specifier
runs catdo with no specifier, to lists all available specifiers for
dodep and catdo, in the form of catdo commands, each of which print
out the do script for a specifier.

Do scripts can be any executable file.  Credo provides only one
parameter to the do script, the name of the target to create.
Credo expects each do file $target.do to create a file $target,

Credo leaves it up to the do script to create its target file, assuming
nothing about its file descriptors.  Credo relays standard output and
standard error to the controlling terminal, and presents nothing on
standard input to the do script.

Dodep assumes as much dependency information, for each type of file
production, as it can without being annoyingly wrong.  It expects
higher-level scripts to use other tools in the suite¹ to program
remaining dependencies, and set values of shell variables specific to
the environment.²
 ¹ For example, adddep, rmdep, addenv, and rmenv.
 ² For example, $cc stores the path to the C compiler on a particular
build machine.  $cflags records the compiler flags used while
producing object files from a specific set of source code files.