Test all features

Tests now permute all features so we hopefully hit all code paths. Well, most tests. Some tests (like aol, lz4, prefix matching) depend on certain features enabled so those are not permuted.

- AOL file is now unlinked after each test where it is enabled
- I added a feature to toggle `fflush()`ing the AOL file (fsync is probably good enough in most cases)
- Fixed some typos