Allow append/prepend API for function bodies / Expose nodes modules

[Exagram]

Are we able to get append/prepend API for inserting calls in function bodies? Currently the append/prepend API only works for the tree body.

Example:

function test() {
    foo('test');
}

Fails: c.body.node[0].body.append('bar();').

So I looked for workarounds. I tried to manually push this new call into the body array via c.body.node[0].body.body.push('bar();'). But doing so fails because bar(); is a string and not an esprima object. A possible solution is to expose AST-query nodes modules so we can do the above. Or add documentation that the body array requires an esprima object.

I can code this change, just need vision.

[SBoudrias]

Hey, can you clarify what you're doing and what is the result you'd expect? Also, when you say something fail, it'd help to have the error trace you're seeing.

A PR is welcomed, looks like you'd just need to make the body node append and prepend function more flexible.