[lua/en] Normalised Lua's doc to a width of 80 characters

When this was originally written, it was written for a line-width of 50 characters, however Learn X in Y Minutes' site is designed for 80-character widths. I changed some grammar around to make it more readable at the new scale. This also allows for some expansion, as I can tell a lot of brevity came from the 50 character width.

I have no idea if this will actually look okay on the site, as I have no way to preview that.