Use dub to create source lib and executables

[Chris Piker]

Hi D

I normally work in a *nix environment, typically on server-side 
code.  For many projects I have gnu makefiles that build a small 
lib along with command line utilities.

Up to now I've been creating a dub.json file for just the 
sourceLibrary, and then putting embedded dub comments at the top 
of each of the utility programs.  The utilities are built via  
`dub build --single` and a thin makefile triggers all the dub 
commands.

This method is inefficient, and it won't work in a typical 
Windows dev environment, so today I'm trying to remove gnu make 
from the picture.  Going back to basics, does anyone know of a 
clear example of how to convert this simplified makefile into 1-N 
dub files?:

```makefile
# Build library + utility programs.
# Lib sources are in "libsrc", 1-file programs in "utils"

# Implicit rule to make a utility program
outdir/%:utils/%.d outdir/mylib.a
     dmd -I libsrc -od=outdir -of=$@ $^

# Top level build rule for everything
build:outdir/mylib.a outdir/prog1 outdir/prog2 | outdir

# Explicit rule to make output directory if not present
outdir:
     @if [ ! -e outdir ]; then mkdir outdir; fi

# Explicit build rule for the library
outdir/mylib.a:libsrc/mod1.d libsrc/mod2.d
     dmd -lib -od=outdir -of=$@ $^
```
This is a paired down example since `make test` and `make 
install` aren't present, but I hope the main ideas are apparent.

I've been at it now for about four hours, with lots of 
web-searches (btw, thanks to schveiguy for getting me this far) 
but I haven't figured out what hierarchy of dub constructs I need 
to create to order to get the effect of the small make file above.

Thanks for considering the question,