lalpulsar/doxygen: fix inline math, add missing groups

Description

• Make sure that \f$ math command is surrounded by spaces
  • See issue #632 (closed)
  • Doxygen is fine with this:

    \f$\mathcal{F}\f$ -statistic

    but doesn't like this:

    \f$\mathcal{F}\f$-statistic

    (note the missing space)
  • Since extra spaces aren't noticeable in formatting, play it safe and always use spaces around \f$
• Add missing \addtogroup @{ ... @} directives
  • Required to include function documentation defined in .c files, esp. inline function argument documentation

API Changes and Justification

Backwards Compatible Changes

• This change does not modify any class/function/struct/type definitions in a public C header file or any Python class/function definitions
• This change adds new classes/functions/structs/types to a public C header file or Python module

Backwards Incompatible Changes

• This change modifies an existing class/function/struct/type definition in a public C header file or Python module
• This change removes an existing class/function/struct/type from a public C header file or Python module

Review Status

Closes #632 (closed)

cc @david-keitel