ENH: Allow a trailing COMMA or PERIOD in a See Also function list block

[pvanmulbregt]

Addresses #206.

Only trigger the trailing comma warning if there is also a description on the same line.
Added a test that the warning is generated.

It supports the following formats.

 <FUNCNAME>
 <FUNCNAME> SPACE* COLON SPACE+ <DESC> SPACE*
 <FUNCNAME> ( COMMA SPACE+ <FUNCNAME>)+ (COMMA | PERIOD)? SPACE*
 <FUNCNAME> ( COMMA SPACE+ <FUNCNAME>)* SPACE* COLON SPACE+ <DESC> SPACE*

Observing a COMMA or PERIOD followed by a (as in the following) is accepted but triggers a warning:

 <FUNCNAME> ( COMMA SPACE+ <FUNCNAME>)* (COMMA | PERIOD)? SPACE* COLON SPACE+ <DESC> SPACE*

Does this cover all the currently desired use cases?

[rgommers]

Great, thanks @pvanmulbregt!

Looks good, and I have tested on NumPy and SciPy docs - all works as expected.