second beta with serialization and hashing options

Second beta BplusDotNet added last night.
This release adds index variants using serialization and hashing.
The serializing variants store and retrieve any serializable object automatically.
The hashing variants arbitrarily large key sizes using a hashing scheme which is immune to
key prefix collision issues, but does not support dictionary order traversal of keys. Various
other issues are tidied up also. Thanks for the suggestions!