Refactor LzfDecoder to use proper state machine

Motivation:

Make it much more readable code.

Modifications:

- Added states of decompression.
- Refactored decode(...) method to use this states.

Result:

Much more readable decoder which looks like other compression decoders.
Allowing negative keys in IntObjectHashMap.

Motivation:

IntObjectHashMap throws an exception when using negative values for
keys.

Modifications:

Changed hashIndex() to normalize the index if the mod operation returns
a negative number.

Result:

IntObjectHashMap supports negative key values.
Optimize IntObjectHashMap handling of negative keys.

Motivation:

The hashIndex method currently uses a conditional to handle negative
keys. This could be done without a conditional to slightly improve
performance.

Modifications:

Modified hashIndex() to avoid using a conditional.

Result:

Slight performance improvement to hashIndex().