[Proposal] Make "End Namespace" optional

It's common practice to have single class, interface, module per file so it's rare case that we need two namespaces in single file, i can think only that in case of generated files it may be usefull to have multiple namespaces per file.

So instead of writing:
```vb
Namespace Sample
Class Test
End Class
End Namespace
```
it would be nice if it could be written as:

```vb
Namespace Sample
Class Test
End Class
```

In case that there are two namespace in file, starting new namespace should implicitly close previous one, so in next example we would have Sample1.Test and Sample2.Test classes.
```vb
Namespace Sample1
Class Test
End Class

Namespace Sample2
Class Test
End Class
```
Update:
1. Mxing namespace styles in same file would not be allowed

2. Nesting namespace is just new namespace with full name
```vb
Namespace One
Namespace One.Two
```