Add option to force the visual mode

[vE5li]

This PR gives users the ability to specify a visual mode when selecting a text object.

With this it is possible to more closely mirror the behavior of the builtin text objects, e.g. vip will always go into line-wise visual mode and vib will always go into char-wise visual mode.

While I was at it I also did a very small cleanup of the documentation, mainly removing some trailing spaces and using lua functions directly instead of wrapping them in "<cmd>lua ..."

[kiyoon]

You can ignore the failing tests, as it's the first PR I think it wasn't tested before.
Make sure you format with Stylua, and luacheck can be ignored.

[vE5li]

When running stylua lua -f stylua.toml in the root of the repository, it changes a lot of code, even files that I didn't touch. Do I need to invoke it differently?

Also, looking at the output of the format check, it looks like the stylua binary is broken or something?

[kiyoon]

OK, maybe I forgot to delete it. The CIs are just copied from indent-blankline.nvim and not tested yet apparently. Just leave it and I'll need to review it later.

Thanks for your contribution! Although I haven't tested it myself it seems to be alright.

Does operator-pending mode work with the new settings? (dai, diI etc.)

[vE5li]

Does operator-pending mode work with the new settings? (dai, diI etc.)

Works like a charm :)