Contains three targets - info, package and clean:
- info creates the info manual for the package.
- package creates an installable (via 'M-x package-install-file')
package archive.
- clean cleans any "build artefacts".
The default (all) target is equivalent to the clean target followed by
the package target.
Add 'config.mk' for build configuration.
Add 'elpher-pkg.el' (could possibly be generated in the future),
required to install as a package.