Kill the cat
[DNM] Make AliasGroup constructor parameter optional
Reworked all equals methods
Merge pull request #292 from wmde/aliasGroupNull

[DNM] Make AliasGroup constructor parameter optional
Merge pull request #249 from wmde/killacat

Kill the cat
Merge pull request #298 from wmde/equals

Reworked all equals methods
Reworked all isEmpty methods
Add tests
Merge pull request #297 from wmde/isEmpty

Reworked all isEmpty methods
Add two more filter methods to StatementList
Avoid in_array