Adding support for searching specifically for an option, e.g. "-i" or "--ignore-case"

In man pages, I often want to search for a specific option, e.g. `-i`, but if I just search for "-i", I often don't get to that option right away. Thus, I have to type in something like `^\s*-i`, which is almost as inconvenient as just hitting "n" a bunch of times and hoping I reach the -i option sooner rather than later.

It'd be great if `mangle` allowed a convenient way to indicate searching for just an option.

I propose something like `mangle grep opt -i`, where the "opt" is a special "pattern" that turns the "-i" into `'^ *-i[, ]`.

I seem to have gotten a prototype working. See: https://github.com/Flurrywinde/mangle/commit/8050fc942e567542ff1ba4d0de546378af17487f