Update asset-compilation docs to cover Babel 6.X transpilation

[BrianSipple]

Following our move to Babel 6.X, I figured it would be useful take a stab at updating the JS Transpilation section of our Asset Compilation page.

I included some insight on babel-preset-env, targets, and how to configure each.

One thing that's omitted, though, is how some Babel features beyond the purview of babel-preset-env can still be controlled by passing options to the ember-cli-babel hash on the app object in ember-cli-build.js.

I can expand on the docs here to mention this, but I'm also wondering if it might be better to fully document those options in the ember-cli-babel README, and then just link to them from here.

[stefanpenner]

Wow thanks!

[kellyselden]

Do we want to keep this section and say "If you're still using ember-cli-babel 5, do it this way"? Is it reasonable to eliminate this section so soon after we switch to 6?

[BrianSipple]

I can see that being a concern, but my thinking was that keeping the link to the 5.x docs would be an adequate way to guide users who haven't upgraded yet.

Also, this is just my take, but I think one of the main use cases for this documentation, in particular, is to guide someone who's newer to Ember and give them an overall feel for Ember CLI. Thus, they're more likely to be on a newer version -- and we're more likely to help them by linking to relevant projects (in this case, ember-cli-babel) for more thorough documentation.

[kellyselden]

Thanks. Sorry it took so long.