test: move the reinterpretUntilZeros() tests to their own file
src: allow Buffers returned from `reinterpretUntilZeros()` up to `kMaxLength` bytes

Fixes a bug where the returned Buffer could have truncated data.

Reported via email by Adam Mansour (@intelligo).
gitignore: ignore root-level single-letter file dev files
v0.3.1