Hash::FieldHash provides the field hash mechanism which supports the inside-out
technique.

You may know Hash::Util::FieldHash. It's a very useful module, but too complex
to understand all the functions and only available in 5.10. H::U::F::Compat is
available for pre-5.10, but it seems too slow to use.

This is an alternative to H::U::F with following features:

Simpler interface
- Hash::FieldHash provides a few functions: fieldhash() and fieldhashes().
  That's enough.

Higher performance
- Hash::FieldHash is faster than Hash::Util::FieldHash, because its internals
  use simpler structures.

Relic support
- Although Hash::FieldHash uses a new feature introduced in Perl 5.10, the uvar
  magic for hashes described in "GUTS" in Hash::Util::Fieldhash, it supports
  Perl 5.8 using the traditional tie-hash layer.