Usage and PreOptions text should have blank lines before them

[asherber]

A plain vanilla help screen looks like this:

MyApp 1.0.0
Copyright 2019

  -o           Operation to be performed

  --help       Display this help screen.

  --version    Display version information.

If I add usage, it looks like this:

MyApp 1.0.0
Copyright 2019
USAGE:
Delete the frobber:
  CommandLine -o Delete

  -o           Operation to be performed

  --help       Display this help screen.

  --version    Display version information.

If there are parsing errors, it looks like this:

MyApp 1.0.0
Copyright 2019

ERROR(S):
  Option 'foo' is unknown.
USAGE:
Delete the frobber:
  CommandLine -o Delete

  -o           Operation to be performed

  --help       Display this help screen.

  --version    Display version information.

The default builder adds blank lines in between most sections, which improves readability -- but not before the USAGE section. I think all of these would look better with a blank line before USAGE.

The same is true of PreOptions lines, which by default show up directly under the copyright line -- they should have a blank line before them as well. (PostOptions lines already get a blank line before them.)

I'm happy to work on a PR if this suggestion is acceptable.