Include default values in help string

[ewu63]

Description

We currently only include default values in a few places, but we should do it for all defaults. This can be done in one of two ways:

• if there are only a few of these, we can just manually add them with placeholder text as I did in Clean up help string #36
• if there are a lot more, we will want to do this programmatically. See this thread for some options. We also have to be careful since we probably don't want to print all the default: None stuff everywhere.

[akleb]

Also, typo in help string for split: witll -> will