Glossary: add "crate" and "module"

[cmcqueen]

Please add "crate" and "module" to the glossary. As someone coming from Python, I'm a bit unsure of what Rust terminology to use instead of Python's "package".

[ehuss]

Yea, it definitely can be confusing, especially when the same term is used in different ways. I have posted #1016 with some definitions. You may also find some definitions in the Cargo glossary for crate and package.

The following is a rough translation:

Python	Rust
project	package or project (a Cargo concept)
root package	crate or "crate root"
subpackage	module
module	module

Rust does not differentiate between leaves and nodes in the module tree, it just calls them all "modules" whereas Python calls inner nodes "subpackages".