Expose and document `inplaceWith` (or some variation of it)

[Ashlynn Anderson]

It would be useful to have some function exposed like inplaceWith that allows you to give a function Shell Line -> Shell Line and use it to modify a file in-place without having to essentially reimplement inplaceWith.

I don't think inplaceWith is the right function as it is, but if you removed the assumption that the Shell Line -> Shell Line function given to it also takes a pattern it would become very useful and only require minor changes to the exposed inplace{Prefix,Suffix,Entire,} functions.

[Gabriella Gonzalez]

The fix is up here: #404