Update docs for v4

[paulfalgout]

@marionettejs/marionette-core as promised I've finally finished doc modifications. I am well aware that this is a huge PR and likely unmanageable as far as reviewing. My suggestion would be to skim it, and unless there's anything big we can make changes in subsequent PRs as we alpha/beta v4.

There was one tiny functional code change explained on the commit: d4330ec

The other changes to src files are changes that are either code comment updates or URL updates for errors.

This work does a few things:

• Updates md code samples to ES6
• Adds a flow to the documentation such that you can start an installation and continue to click to somewhere meaningful in the docs.
• Makes the docs match more of the code structure.. this is the big change and the important one.. we were getting a lot of duplication and it was hard to tell where to add docs when a feature was added. It isn't an exact science now, but it is much, much more clear where new docs will go.
• Links thrown errors to docs about the error and makes a note about the error in the docs (we'll want to keep this up)
• Updates everything for v4 changes
• Standardizes similar language between related but different classes. The way we outline dealing with child views is now similar between the region and view docs. This helps the reader intuitively see the similarities, but highlights the differences.

What this doesn't do:

• Address the v4 upgrade guide (might be best to leave this until we're ready for beta to be complete)
• Address any other docs.. main readme, contribution, unit tests.. all of those are probably somewhat outdated.
• Update the jsfiddle samples (as there's no public lib at the moment)

Once this gets in I'll make an alpha branch 🎉

If you want to visually click through: https://github.com/paulfalgout/backbone.marionette/blob/doc-updates-views/docs/basics.md

[coveralls]

Coverage remained the same at 100.0% when pulling d7772bf on paulfalgout:doc-updates-views into 5e1466e on marionettejs:next.

[paulfalgout]

I think this PR addresses: #3320 #3595 #3596 and #3606

[JSteunou]

That's a lot of work! I'm all in to merge this and fixing / rewording afterward, but even until this, it already looks amazing!

[JSteunou]

typo: collection changes,

[blikblum]

Nice work

[blikblum]

Address the v4 upgrade guide (might be best to leave this until we're ready for beta to be complete)

I can help with that. See #3447. Must settle on a format