Remove warnings

[luciansmith]

• sprintf->snprintf
• Addresses of actual objects are never NULL
• 'this' is never NULL
• Add default cases for ASTNode switch statements.

[fbergmann]

looks good to me though it seems odd, that we have different array lengths in our code base.

and i'd much rather see the use of normal stl instead, like std::to_string rather than snprintf.

and the group thing, since isSetGroup always return true, we really dont need to check for isSetGroup ever.

[luciansmith]

Yeah, I left in the 'isSetGroup' function just in case we changed our implementation in the future. Like, perhaps we'll want to check if anything is non-default in the 'group' object, and only write things out then?