Performance improvement suggestion

[tobiu]

Hi @onury,

i just played a bit with jsdocx.filter().

for building https://github.com/neomjs/neo JSDoc can return 14.000+ items (this task takes around 2s).

the call:

https://github.com/onury/jsdoc-x/blob/master/src/index.js#L285

docs = _.reduce(docs, (memo, symbol) => {/**/});

ended up with 140s+ on a very fast machine.

I added the following change locally:

if (!options.undocumented) {
    docs = docs.filter(symbol => {
        return !symbol.undocumented || utils.isConstructor(symbol)
    });
}

docs = _.reduce(docs, (memo, symbol) => {/**/});

this pre-filtering reduced the amount of items from 14k to 2.7k and the following reduce call from 140s to 3s.

we could probably get a bit faster with replacing _.reduce with Array.reduce(), but this one was at least for me the main bottleneck.

adding the change to the lib would be appreciated (will use an override for the mean time).

thx & best regards, tobias