Support for wrapping the usage declaration

[stefmolin]

I am trying to use this with a CLI that has a lot of configuration options, so when I render the usage section it requires a lot of horizontal scrolling:

I hacked something to wrap my output, but I was wondering if this could be incorporated into the library as an option (maybe something like :width: 80 for 80 character width):

I'm happy to help if this is of interest and some pointers as to where to start could be provided.