Add method to frame and center header

[Magnum97]

First of all, thank you for this library. It is great to have a YAML lib that supports comments and is extremely easy to use. My favorite feature is the 'orDefault' set. :+1:

Here is something I wrote to spice up my headers. An example:

This line framedHeader("Line one","This is a longer line","This is going to be a super long line!!");

Produces the following header:

# +----------------------------------------------------+ #
# <                      Line one                      > #
# <               This is a longer line                > #
# <      This is going to be a super long line!!       > #
# +----------------------------------------------------+ #

I look forward to any feedback.

[KotlinFactory]

We just reviewed your code.

Thank you so much for the kind feedback & adding this!