Implement ignoreEval option to analyze. Fixes #2.

[glasser]

We want this because we want J in

function () {
  var J;
  J = 3;
  eval("foo");
}

to count as resolved! I'm really not sure why it isn't just because there's an eval there...

[Constellation]

Hi, thanks for your request.

Direct call to eval can create variable to the local scope, so if there's eval we cannot analyze precise scope

function outer() {
    var i = 42;
    function inner() {
        eval('var i = 0');
        i;  // 0, not 42
    }
}

Direct call to eval can take string, so we cannot analyze it statically.

Escope guarantees precise scope analysis, this is the most important for some tools need precise analysis, such as minifiers. So if it encounters eval, annotating scope direct scope and gives up analysis.

But some tools don't need precise analysis, for such tools we should provide this option.

[Constellation]

We need consider API interface name, so this ignoreEval option name may be changed when escope is released.

[glasser]

Ah, got it. So an eval can make a reference be TIGHTER than you would imagine.

For my particular use case I only really care about implicit global variables, so the only thing I'm concerned about are references that are LOOSER than they look, so ignoreEval is OK. (See #17 for why I don't just look at the global scope...)