Check that histories directory exists before trying to create.

[glenpike]

Add post-install script that should be cross-platform.
Closes #18

[alidavut]

Looks good to me. I think we can merge this and wait #17 for the other things.

And maybe you would like to use a module for cross-platform like https://github.com/substack/node-mkdirp

[glenpike]

I was hoping it was cross-platform just using the built-in libs, but not easily able to test on Windows.

[alidavut]

I didn't remember if windows has 'mkdir' command, seems it has. Let's merge if ok for you?

[glenpike]

Happy with that - I looked it up, but I wasn't able to test.

[HuangChaoWH]

Hi, I released a private package:
@huangchaowh/locus
it works on Windows.
It change the postinstall to "mkdir histories".

[glenpike]

@HuangChaoWH I don't think that fixes the initial problem which is that the postinstall fails if the directory exists. I am guessing you made a new postinstall rather than testing the one in this PR, but I maybe wrong?

[glenpike]

Is there any chance of getting this reviewed, merged and published?
Everytime I have to rebuild my node stack, it fails because this directory exists and that's not a quick process.