Change YARD doc formatting to follow my style more closely
Add whitespace after last method
Remove injected cache from the Memoizable::Memory constructor

* It turns out that it isn't necessary to inject the cache into the
  constructor while loading the cache data.
* Fix documentation on the #marshal_load method to make it clear
  that the return value is not used by Marshal.
Change YARD description for marshal hooks to be more descriptive
Remove unnecessary helper method

* While the method does allow two other methods to eliminate one
  line of code each, I think I prefer the code here instead. The
  extra indirection seems unnecessary, and I don't like how long the
  lines of code became when used with lots of arguments.