Re-review and improve documentation

[janbridley]

Description

• Documentation for the PATTERNS class variable -- which can be edited by users to enable parsing of standard-noncompliant files -- has been improved with additional details on the relationship between patterns and their corresponding grammatical features.
• repr now includes a copy-pasteable string for initialization
• Minor changes to several docstrings
• Add example for HOOMD-BLue
• Add example for LAMMPS
• Add example for numerical precision

Types of Changes

• Documentation update
• Bug fix
• New feature
• Breaking change¹

¹The change breaks (or has the potential to break) existing functionality and should be merged into the breaking branch

Checklist:

• I am familiar with the Development Guidelines
• The changes introduced by this pull request are covered by existing or newly introduced tests.
• I have updated the changelog and added my name to the credits.