Added manuals

> Renamed "Manual" folder and namespace to "Manuals" for consistency;
> Pretty much finished the manuals system;
> Made manual system optional when adding default commands;
> "man" command has pretty much every feature in its scope;
> Wrote a nice manual for the "man" command itself;
> Added manual drivers - objects in charge of displaying manuals;
> Added a default manual driver which outputs the manual's contents in a
nice and human-readable way.

More manuals are going to be written soon.
The XML schema is very elegant and I will continue to use that.

The manual drivers allow a (library) user to display manuals in
arbitrary ways, such as using Windows Forms.