Added suite design guide, tidied doc directories.

[hjoliver]

As discussed with @dpmatthews and @arjclark - this adds the new Suite Design Best Practice Guide to Cylc, and reformulates doc/Makefile to handle that as well.

Also removes the now-obsolete "Suite Design Guidelines" and "Style Guide" sections from the user guide.

[hjoliver]

@matthewrmshin - this is documentation only (albeit quite a lot of it) - but assign a 2nd review if you like.

[hjoliver]

(Matt, you probably don't need to review the new document - it has been reviewed at length by Dave, Andy, and others, over the course of ~3 months ... in case you're not aware of that)

[matthewrmshin]

Looks OK. 2 minor issues:

• Can we ensure that the items that are created by make are ignored by git status?
• doc/index.html no longer works after this change. Can we have it redirect or else?

[hjoliver]

Can we ensure that the items that are created by make are ignored by git status?

Done

doc/index.html no longer works after this change. Can we have it redirect or else?

That file should no longer exist. All the generated files should end up here:

$ ls -1F doc/install/
cylc-user-guide.pdf
graphics/
html/
index.css
index.html
suite-design-guide.pdf

[matthewrmshin]

Good to go.