doc (book)[01/14]: glossary beef-up

doc (book)[01/14]: glossary beef-up

Add a handful of entries to the glossary of The Cargo Book, and add
intra-glossary hyperlinks for terms. A full catalog of the specific
changes follows.

Glossary entries added:

    + 'Cargo.lock' -- just points to the 'lock file' entry

    + 'Cargo.toml' -- just points to the 'manifest' entry

    + 'Module' -- explained in relation to 'crate'

    + 'Package manager' -- first term in the Introduction

    + 'Package registry' -- Another term from the Introduction. This
       entry just points to the 'registry' entry

Glossary entries modified:

    + 'Artifact'
        - Extend def. to include generated docs.

    + 'Crate'
        - Refer to a "Rust crate" as a hint that it is a term that
          exists outside of Cargo.

        - Refer to a "Cargo package" (rather than just "package") to
          reflect the fact that the term is a concept introduced by
          Cargo (as opposed to being inherent to Rust).

        - Link to related terms: 'module', 'package', 'registry',
          and 'target'.

    + 'Edition'
        - Link to related term: 'manifest'.

    + 'Feature'
        - Link to related term: 'manifest'.

    + 'Index'
        - Markdown: add emphasis to first mention of term "index".
        - Link to related terms: 'crate', 'registry'.

    + 'Lock file'
        - Link to related terms: 'package', 'workspace'.

    + 'Manifest'
        - Link to related terms: 'package', 'workspace'.

    + 'Member'
        - Link to related terms: 'package', 'workspace'.

    + 'Package'
        - Note that every target is a crate, and that the type
          (library or binary) is determined by the Cargo.toml file.

        - Note relationship to workspaces.

        - For "package root", add "compare to" note referencing
          "workspace root".

        - Link to related terms: 'crate', 'manifest', 'target',
          'workspace'.

    + 'Registry'
        - Link to related terms: 'crate', 'index', 'package'.

    + 'Source'
        - Link to related terms: 'crate', 'package'.

    + 'Target'
        - Link to related terms: 'artifact', 'manifest', 'package',
          'workspace'.

    + 'Test Targets'
        - Link to related terms: 'crate', 'manifest'.

    + 'Workspace'
        - For "workspace root", add "compare to" note referencing
          "package root".

        - Link to related terms: 'lock file', 'manifest', 'member',
          'package'.