Fixed documentation for common families

[janbridley]

Description

A few of the families defined in #177 have messy documentation that result from missing line breaks. This has been addressed, and the short docstrings (which display in the Classes table on readthedocs) have been made more uniform.

Types of Changes

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

¹The change breaks (or has the potential to break) existing functionality.

Checklist:

• I am familiar with the Contributing Guidelines.
• I agree with the terms of the Contributor Agreement.
• The changes introduced by this pull request are covered by existing or newly introduced tests.
• I have updated the changelog and the credits.
  ^{These changes fix a PR that I authored, so I have not modified the changelog.}

[codecov]

Codecov Report

Merging #191 (0823466) into master (6e5331d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #191   +/-   ##
=======================================
  Coverage   54.78%   54.78%           
=======================================
  Files          26       26           
  Lines        2621     2621           
=======================================
  Hits         1436     1436           
  Misses       1185     1185           

Files Changed	Coverage Δ
coxeter/families/common.py	32.14% <ø> (ø)

[DomFijan]

Looks good, Some of the name docs don't render properly (at least they are not in line with how others look). I think you are missing an empty line. Once this is fixed this is ready.