Adjust comments and whitespace to more closely match coding standards

I've run the Pathauto module through PAReview as well as my IDE's code inspector, and found a number of issues with the whitespace and comments in the module, including typos and incomplete docblocks. I've fixed what ones of these I feel I can in the included patch.

The only included code change which is not simply whitespace or in comments is an argument name in the constructor of PathautoGenerator; it was $token_entity_mappper, with an extra "p", so since I was newly adding documentation of this argument I thought it better to fix the typo rather than to replicate it in the docblock.

This patch is not comprehensive in its docblock changes, but it should certainly get the module a good deal closer to meeting current Drupal coding standards.