Get compiling on rustc version 0.10-pre (de78d7f 2014-03-15 17:51:35 -0700)

- use new librand instead of std::rand (which was moved to librand)
- can't match on ~str anymore; have to use as_slice() and match on &'static str instead
- use vec_ng::Vec instead of ~[]; vec! macro for initialization, as_slice to index

Still have warning for usage of deprecated ~[] vector because os::args() hasn't been
updated to to use vec_ng::Vec yet.
update README "compiles with" statement for latest rustc (de78d7f)