Add npm prepublish support

[mattnibs]

With our current setup we were running into a couple issues when importing juttle-viz into other libraries. 1) We couldn't import and browserify the library because we weren't babelify the source and 2) We weren't generating a javascript blob that I can throw into my browser.

What I did here:

• Created gulp lib task that run all js code through babel and spits it out into a lib dir. As such I've pointed the entry to lib/index.js. Now requiring juttle-viz should "Just Work"(TM).
• From the above had to rename folder lib in src to ext so my .gitignore on lib wouldn't remove lib from src/lib. I don't think src should have a folder called lib anyways.
• Add a gulp clean command that removes generated dirs (lib, build and test/build)
• Add an npm "prepublish" script that cleans the repo then generates the babelified lib and browserify artifact.

Moving forward: Kind of weird that babel has two different libraries: gulp-babel and gulp-babelify. Ideally we create the artifact and lib using the same babel lib. In a future pr we might want to use webpack while might give us the flexibility that we need.

[mattnibs]

@rlgomes @demmer (if @go-oleg is still around)

[go-oleg]

@mnibecker, thanks...definitely need to have build artifacts that can be included in the browser or required.

Some thoughts/questions:

• I haven't seen the ext convention anywhere...can you point me to a js lib that uses that? If you are trying to prevent .gitignore from ignoring a nested lib folder, you can add /lib in the .gitignore instead of lib. As far as having a lib folder under src, I'm not sure why thats bad. We could move the folders in there to be directly in src or organize them in some other way.
• As far as depending on both babelify and gulp-babel goes, I think if you have browserify work on the output of your lib task, then it no longer needs babelify, so you could get rid of that dependency there.
• Why is the index.js in lib and not in src? sry, misread, it is in src
• Browserify lets you specify transforms directly inside package.json in a browserify property which tells browserify what transforms need to be applied. This is super convenient for consumers of this lib that use browserify to build their applications because they can browserify the whole thing without having to worry about what transforms need to be applied to this specific library. Perhaps adding this to the package.json would be a good idea. I tried to find something similar for webpack but couldn't...do you know if it exists?

[mattnibs]

Thanks for your feedback @go-oleg.

• @rlgomes and I kind of discussed this. I decided to do this because 1) the whole .gitignore thing and 2) with the lib output you would have a folder called lib/lib which I thought was kind of weird. Honestly I think the best solution would be to just flatten the whole thing. I think for right now I'll just keep it lib and we can discuss this at a later date.
• Yeah but then in dev mode you'll have to wait for gulp-babel to rewrite the entire contents of lib, then for browserify to kick off and write its output. Seemed like a lot. I would prefer to ditch gulp altogether and go with webpack which would do this all in memory and be a lot faster and less weird.
• coo
• webpack --config webpack.config.js?

[mattnibs]

@go-oleg I got rid of the whole ext business.

[go-oleg]

snds good!