This patch extends dcmerge to support the command attribut of a defined service.
For example:
```yaml
services:
busybox
command: [ "/usr/bin/cp", "--recursive", "--force", "/tmp/bar.txt", "/tmp/foo.txt"]
image: library/busybox:latest
```
The command attribute is interpreted as a whole. This means that individual
arguments are not merged as a comparison, as this would change the meaning of
the command attribute.
