Migrate to gulp & karma

[danvk]

This is heavily based on (and supersedes) #528.

Highlights:

• Moves all code into src/
• Switches from jstd to Mocha, Chai and Karma.
• Uses gulp for building

The upshot is that dygraph becomes a more modern JavaScript library and we can start using nice tools like Istanbul (for code coverage) and Babel (for ES6/7→ES5 transpilation).

[coveralls]

Changes Unknown when pulling fbab47f on gulp into * on master*.

[coveralls]

Changes Unknown when pulling 08391a4 on gulp into * on master*.

[danvk]

@kberg @klausw-g @flooey FYI

This is a fairly big change to dygraphs—see PR description. I'd like to merge this in relatively soon (tonight or tomorrow), so please let me know if you have any objections.

[coveralls]

Changes Unknown when pulling e8a0d6a on gulp into * on master*.

[coveralls]

Changes Unknown when pulling b0ce973 on gulp into * on master*.

[flooey]

It looks like this only changes the build process, not any of the code, right? If that's the case, it'll be a bit annoying to set up the next time we update our copy, but should be fine otherwise. Feel free to go ahead.

[danvk]

That's correct. To get the same file as before, you run:

npm install
gulp dist
ls dist/dygraph-combined.js

dygraphs already depends on NPM, so this shouldn't be a big deal.

If anyone depends on individual JS files in dygraphs, they'll have to be updated. But I'd highly recommend not doing that. I plan to start using ES6 features soon, which will make these files not directly includable in the browser.

[danvk]

Okie doke, this is going in.