ASAN and vfork() don't appear to play well together. Maybe in later
versions of GCC it'll be better. But vfork() is flirting with danger
after all and that probably doesn't make sense in ASAN mode anyway.
Buffering now has optimal performance, bugs have been fixed, and some
missing apis have been introduced. This implementation is also now more
production worthy since it's less brittle now in terms of system errors.
That's going to help redbean since lua i/o is all based on stdio.
See #97
