Blank lines interpreted incorrectly within Virtual Methods and Overloads

This PR fixes the below example.

```coffeescript
# My Special Class
#
# A very special class I wrote.
#
# @method #get(key)
#   This is the initial summary.
#
#   This is a second line to the summary.
#   And a third.
#
#   @param [String] key the key you'd like to retrive the value of.
#
#   @example Get the value
#     msc = new MySpecialClass()
#     valueOfFoo = msc.get 'foo'
#     # now do whatever you please with valueOfFoo!
#
class MySpecialClass
```

In the above example, the current codo behavior is to stop processing the `@method` once it hits the first blank line. This can be remedied by simply putting a # and two blank spaces, however, many text editors automatically remove trailing white-space in source files, so your documentation is therefore very brittle.

This PR fixes this behavior by continuing to process the `@method` even when we find blank lines separating other meaningful lines.

I also duplicated this behavior for `@overload`.

Additionally, I wrote tests for each to support the change.

The relevant changes to codo code are in doc.coffee and are to the below listed lines:
[doc.coffee:217](https://github.com/netzpirat/codo/pull/124/files#L5L217)
[doc.coffee:238](https://github.com/netzpirat/codo/pull/124/files#L5L238)