Add expm support

This change will allow Robert to execute ``make upload`` and publish LFE to expm.co:
  * http://expm.co/

Note that in order for that to work, one will need to:

1. create an EXPM username : ``./bin/expm config:set username rvirding``, and
1. create an EXPM password: ``./bin/expm config:set password something-great``

There is a make target ``get-version`` which offers a sanity check that the ``.app`` file version and the ``.exs`` file version are the same. This is automatically called when performing the upload with ``make upload``.

Once published, a page for LFE will be created like this one for loise:
 * http://expm.co/loise

On this page, users can copy and paste the configuration setting that is pertinent to their chosen method of dependency management.

Also, using ``expm`` from the command line, users will be able to do such things as this:
```
$ ./bin/expm search lfe
lfe-utils            Utility functions for LFE
lfeunit              An eunit clone for LFE
loise                A Noise-Generator for LFE
```