Set proper inner dependency

[alindl]

Setting this dependency, allows maven to do parallel builds, obviously improving building times. asterix-doc needs at least one file (SQLPP.HTML) that is build by asterix-lang-sqlpp.

[parshimers]

Wow! This is great, Thank you.

I tried to get this to work a long time ago, but I guess I was barking up the wrong tree. I thought it was because the javacc-maven-plugin didn't properly support parallel maven execution.

[alindl]

I just figured that there's an error because asterix-doc just plainly copies stuff from asterix-lang-sqlpp. It's even noted here, so that comment tipped me off, that maybe we need to build asterix-lang-sqlpp before we can copy something from there 😉