Add more support for camelcase()

@svetosch asked for the following feature

~~~
I meant the direction go_gretl -> GoGretl.
~~~

### The starting point to think about

I don't mean yet another function, but an _option_, something like this:
~~~
function string camelcase (string input, string sep[null])

  string sep = exists(sep) && strlen(sep)==1 ? sep : " "    # blank is
default
~~~