export to Makefile

[UnixJunkie]

I thought it was in the wish list already, I opened this as I cannot find it back.
Exporting the build commands to a Makefile might allow users to release their software
without requiring end users to install obuild.
Maybe a command like 'obuild build --makefile' could dump a valid makefile to stdout.

[UnixJunkie]

@c-cube also thought about dumping to a .sh directly (that would not allow to paralellize
the build but at least a workaround for people who don't have obuild installed).

[UnixJunkie]

dumping commands to a .sh file is strongly related to the -n option I think.
-n is in fact dumping to a .sh which is /dev/stdout

[UnixJunkie]

related to #143

[UnixJunkie]

There may be students starting from September that will work on this.

[UnixJunkie]

The first step is to be able to export to a bash script:
#145