#586 add hoisting check to no-unreachable

[makepanic]

Added check for no-unreachable if node has:

• node.type equals FunctionDeclaration
• node.type equals VariableDeclaration and every declaration has no init

I also added some tests that verify the new implementation and refactored the initial loop to a function to avoid repetition. This pull request should resolve #586

If there's anything wrong feel free to tell me.

[nzakas]

Nice, I like this abstraction. Can you add some doc comments to it?

[nzakas]

Can you also add some details in the rule documentation explaining this case?

[makepanic]

I added a note that describes the cases that don't trigger the no-unreachable warning and added jsdoc comments.

[michaelficarra]

The control flow in this function is beyond odd. Use this instead:

function isUnreachableAllowed(node) {
    return node.type === "FunctionDeclaration" ||
        node.type === "VariableDeclaration" &&
        node.declarations.every(function(declaration){
            return declaration.type === "VariableDeclarator" && declaration.init === null;
        });
}

--cyclomaticComplexity;

[nzakas]

Thanks for the fast turnaround on the review comments!