Resource Compiler.

This compiler converts .src files and .hrc equivalents into binary
.res files.  The basic idea is that this provides a map between
integer identifiers and the resources: string, pixmap (only the
file-name), and VCL control properties.

In more detail:

Typically we would have a .hrc file with entries like this:

#define SID_STR_FOO    1234

And then a .src file with some entries like this:

String SID_STR_FOO
{
    Text [ en-US ] = "Foo !" ;
};

This is compiled into a binary resource file, we have many of these
which live in program/resource/ and then tends to get used in the code
thus:

String aStr( ResId( SID_STR_FOO ) );

It is important to note that any appearance of hierarchical structure
in the .src files is in fact a mirage. The file is compiled at root
into a plain map<integer,resource>.

There is some German documentation about it in a subdirectory called
[git:rsc/doku].  Seems to be very old (January 1992).
