This is a more introductory document, suitable for Part II. The arcane details move to an "Advanced macros" chapter in Part III.
Conflicts:
src/doc/trpl/macros.md
@steveklabnik Trying out the Glossary idea.
Added the paragraph about 'complicated words' because I think it would be useful to those contributing to the book. Maybe this should not be here
This pulls all of our long-form documentation into a single document,
nicknamed "the book" and formally titled "The Rust Programming
Language."
A few things motivated this change:
* People knew of The Guide, but not the individual Guides. This merges
them together, helping discoverability.
* You can get all of Rust's longform documentation in one place, which
is nice.
* We now have rustbook in-tree, which can generate this kind of
documentation. While its style is basic, the general idea is much
better: a table of contents on the left-hand side.
* Rather than a almost 10,000-line guide.md, there are now smaller files
per section.
