std.string.remove(Front|Back|First|Last|FirstN,LastN)

I found these function to be quite common when processing strings.

These functions are not hard to implement, but why bother the developer with all the length handling and such.


I think it makes more sense as:
```D
auto eraseFirstN(T,S)(T str, S toRemove, int cnt);
```
As it *adds* an extra parameter to `eraseFirst`.