Slurp defines function in shell

After slurp is called, hello world example should be started with (start) instead of (: hello start).

LFE Shell V5.10.1 (abort with ^G)
> (slurp '"hello.lfe")
#(ok hello)
> (: hello start)
exception error: undef
  in (: hello start)

> (start)
Lfe says 'Hello, World!'
ok
>