* Move overview and introduction files into a single folder
* Remove about_this_book.md We can add a guide to contributing to documentation,
  and mention the book there.
* Remove heartbleed case study This has been a stubbed out article for ~3 years.
  We might consider an article like this for a technical white paper,
  or a blog post, if someone gets inspired.
* Stub out design/drivers and design/memory files
* Remove will redox replace linux
* Differentiate: Philosophy, Why a New OS, Goals

Refs #134

book: add docs for the scheduler

See merge request !147

fixed two typos in documentation

See merge request !145

Book link fixes

See merge request !144

src/explore/explore.md contains a link to a "Utilities" file. This file
no longer exists (it was removed in commit 2854c9b0). In order to avoid
unnecessary 404-type errors, remove the link to this page.

The redox book contains some broken links throughout the various
markdown pages. Fix all broken links to existing pages (by using
relative paths only) such that the documentation can be used as
intended.

This reverts merge request !143

Fix markdown book links

See merge request !143

src/explore/explore.md contains a link to a "Utilities" file. This file
no longer exists (it was removed in commit 2854c9b0). In order to avoid
unnecessary 404-type errors, remove the link to this page.

The redox book contains some broken links throughout the various
markdown pages. Fix all broken links (to existing pages) such that
the documentation can be used as intended.

Fix broken link to 'Compiling Redox' chapter

See merge request !142

Fix external project URLs

See merge request !140

gcc7 is needed instead of gcc49

See merge request !139

Looking at `homebrew-gcc_cross_compilers` at homebrew-gcc_cross_compilers!4 (062060c4), 
it looks like gcc7 is needed and not gcc49.

Fix broken SVG path in boot process

See merge request !138

Signed-off-by: Jérôme Jutteau <jerome@jutteau.fr>

Grammar cleanup

See merge request !137

Changes instances of
>an URL
to
>a URL

Update linux dependencies

See merge request !136

Fix permission denied on libc git clone

See merge request !135

Rewrite some links to HTTPS

See merge request !134

Fix redox releases link

See merge request !133

Update links to point to GitLab where possible

See merge request !132

Add more detail on Sodium

See merge request !131

Some links are not valid as they are only on GitHub (not part of our
team), other links are not valid as some contributors have not logged
into our GitLab yet

I also disambiguated the "Exploring Redox" title that was shared between
a page and a chapter

add packages needed for build

Gave a hint about adding xargo to the path

To help users who haven't previously installed software via cargo

added login information