Split install instructions into separate pages

[ISSOtm]

Also list "static bins" options where available, and clean up some wording.

Fixes #59.

[ISSOtm]

cc @rondnelson99 and @LIJI32 for review.

[ISSOtm]

I see the points @avivace made in his review comment, so I have tried addressing them in the last two commits. (Plus a rebase.) I hope it's satisfactory.

Now that headings are added to each sub-page, I think that it's not a good idea to re-merge everything into a single page, because then that creates a lot of headings in that single page, and I think that'd dilute their value then.

In hindsight, that single sentence summarising three steps makes me feel like the original writing was kind of dumb. Oops.

[avivace]

Thanks for the follow up @ISSOtm . This definitely looks better than before and I think we're getting there..

However:

1. Some pages are now a messy combination of a bunch of boxes trying to get your attention and it feels very confusing to navigate:

2. The MacOs and the Linux manual instructions are basically identical so I don't understand why they were split in two pages. This added complexity over the one page solution we had before which is way more clearer and has less redundant information.

3. The Windows page is now literally 3 lines. Why are why separating pages again and require additional navigation? What is the advantage?

4. I like that Build RGBDS yourself and use a development version are "exposed" in the sidebar. "Building RGBDS yourself" is a strange/uncommon wording though, we should go for a more traditional "Build RGBDS" or "Compiling RGBDS".