Fix documentation formatting

[owen-mc-diffblue]

Getting rid of \par in doxygen

• Each commit message has a non-empty body, explaining why the change was made.
• My contribution is formatted in line with CODING_STANDARD.md.
• Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[tautschnig]

Nit picking: in the commit message, could you be more explicit as to why getting rid of \par is a valuable thing to do (my limited Doxygen knowledge makes me guess that \par has nothing to do with parameters, but might just be a paragraph?).

[allredj]

Passed Diffblue compatibility checks (cbmc commit: f99e3cc).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/87937057

[allredj]

Passed Diffblue compatibility checks (cbmc commit: f4aecf2).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/87957629

[johnnonweiler]

LGTM.