Need directives for optional settings (running list attached)

[Google Code Exporter]

All optional behaviors of propasm should be configurable by directives (and 
optionally overridden 
by command-line flags).  It may be a general directive, like
   .option  name{=value}

or a specialized one, like
    .name value

(I lean toward the general one.)

Behaviors we need to make configurable include:
- Whether read-only registers can be used in the D field.
- Whether res can be used before initialized data.
- Whether explicit alignment is required.

Original issue reported on code.google.com by [e-mail] on 21 Nov 2006 at 5:40