Merge enforceEx with enforce

Makes it possible to call `enforce!MyException` instead of `enforceEx!MyException`, eliminating
redundant notation. Old enforceEx is not deprecated but removed from documentation examples.

This fixes one of very common Phobos "WAT" moments for me - having separate name for semantically identical
function with a different argument set.
The patch looks very boring, I like it.

One question though, would their be any benefit of making the file and line template arguments like so:
```d
T enforce(E : Throwable = Exception, T, string file = __FILE__, size_t line = __LINE__)(T value, lazy const(char)[] msg = null)
```
and passing it like this all the way to bailOut. I would image the compiler could take some advantage of that.