non-native loadstring since rust doesn't natively support it

[SoniEx2]

in some languages you can evaluate the contents of a string. e.g. in python:

# (this is very useful with IRC bots)
exec("def x(v):\n    print('hello world')\n    if v:\n        print('bye world')\nx(False)\nx(True)")
# hello world
# hello world
# bye world

rust can't, so I'd like eval to do it for me:

<Soni> eval: --string "\"foo\\\n                               bar\""
[eval] "foobar"