YARD comments added to 5 lib/msf/base/ files

Added YARD comments to:
  lib/msf/base/config.rb
  lib/msf/base/logging.rb
  lib/msf/base/persistent_storage.rb
  lib/maf/base/persistent_storage/flatfile.rb
  lib/msf/base/serializer/readable_text.rb

~~Added the line --no-private to .yardopts. This will prevent items tagged with @private from displaying in the generated documentation. Very useful for @@variables defined in the class as they are shown as constants in the documentation (see logging.rb for an example of what I mean).~~

Removed leading and trailing empty comment lines when they are in a position that makes YARD parse them. Please let me know if you would like to keep these in the future.

Some information may be wrong. I did my best to track down return types from functions and what should be acceptable as parameters, but I'm only human. 

I plan on documenting everything I can. Please let me know if you would like anything done differently in the future. As I browse the code, I sometimes notice unused parameters/options and empty methods. If you like I can mark them with an `@todo`, `@note`, a custom tag, or something else.