Add support for multiple namespaces

[Nico314159]

Use #namespace preprocessor directive in header. Example below:

#namespace mynamespace

class mynamespace {
    function test() {
        say "This'll be at mynamespace:test";
    }
}
class anotherclass {
    function test() {
        say "This'll be at currentnamespace:anotherclass/test";
    }
}

[WingedSeal]

Would like to change this to #override And remove #override_minecraft in the same commit So you'll now use #override minecraft and #override customnamespace instead

Change header.custom_namespaces to header.overrides or header.namespace_overrides

I can do these changes myself once I have the mood to code again lol

[Nico314159]

I can do these changes myself once I have the mood to code again lol

Just did all of those for you lol, can you LGTM?

[WingedSeal]

lgtm