Solid inner borders modifier

[ModProg]

I would propose the following modifier for the UTF-8 Table:

const UTF8_SOLID_INNER_BORDERS: &str = "        │─         ";

This results in the following table:

┌───────┬───────┐
│ Hello │ there │
╞═══════╪═══════╡
│ a     │ b     │
├───────┼───────┤
│ c     │ d     │
└───────┴───────┘

In Terminal with the lines actually connecting:

[Nukesor]

Nice, looks like a reasonable proposal :)
Feel free to create a PR.

Don't forget to add the change to the CHANGELOG.md and to reference your profile + this issue