mod safe provides iterator-like API with FromSql, ToSql, RowIndex traits atop lib API
 - SqliteRow provides column_count(), with_column_name(), column_int()
 - SqliteRow lifetime incompatible with Iterator trait, unfortunately
 - std::c_str for ??

ack; http://www.rust-ci.org/sfackler/rust-postgres/ for inspiration
move code using `unsafe {}` from lib.rs to `mod core`; move `mod safe` to lib.rs

--HG--
rename : src/lib.rs => src/core.rs
rename : src/safe.rs => src/lib.rs