parallelizing file existance check using promises

[maxlath]

Motivations:

• accessing the file system through sync operation can get slow if there are many files to check
• fs.exists is deprecated since NodeJS v1.0.0

If this sounds like good motivations, I can have a look at other places where fs.existsSync is used throughout the project :)

thanks for this great project!

[claudioc]

This is very good point. I like how this PR works and I definitely would like to merge it.

I propose that you try to kill all the exists, first if you want replacing them with a sync access and then if you feel comfortable with the code, move them to the promisified version.

What do you think? Thanks!

[maxlath]

4d5495f focuses on killing all uses of fs.exists but mostly keeping the sync flow

[maxlath]

Then, getting those to work async seems to require some heavy rewriting. That could make sense in an effort to get the whole project into promises flow but I can't give it the time in needs unfortunately