Review makefile to build SPK

[jdel]

make spk should be working but the postinstall script needs to be reviewed to get composer and install dependencies.

Travis is probably going to fail builds after this...

[jdel]

Also add a test rule so travis can run the tests for us

[mbirth]

Composer needs the phar extension to be installed/enabled for the used php version. Can be checked with (5.6 has it enabled, 7.0 not):

# php56 -i | grep Phar
Phar
Phar: PHP Archive support => enabled
Phar EXT version => 2.0.2
Phar API version => 1.1.1
Phar-based phar archives => enabled
Phar based on pear/PHP_Archive, original concept by Davey Shafik.
Phar fully realized by Gregory Beaver and Marcus Boerger.

# php70 -i | grep Phar
#

There seems to be no easy way to enable already installed (but disabled) extensions. (Would have to fiddle with e.g. /volume1/@appstore/PHP5.6/usr/local/etc/php56/conf.d/extensions.ini) So it's probably better to show an error or a warning or just let postinst fail.