Add istypeof function
Attempting to set a String object's value will throw a valueError if it's not already a basestring
Make DateTime._parse_value a static method for consistency
Add tests for EmailHeader.subject
Add test for 'sender' field.
Convert EmailHeader 'from' and 'sender' from properties to TypedFields

'from' works just like 'sender' so the tests weren't duplicated
Move try_cast to a class property than each instance of that type in a TypedField
Automatically determine dict key name and attribute name from XML name
First attempt at generic (to|from)_(obj|dict) functions

Replaced ReceivedLine's customized version with the base class versions
Allow TypedFields that do not specify an exact type.

No attempt is made to cast these values.
Add list support to generic functions and add support for ByteRun and ByteRuns types
Make Hash class simpler
Add support for additional callback hooks when setting fields
Make round trip test more verbose and improve comments
Clean up EntityList a bit
Simplify some Email lists
Make the default cybox.Entity to/from functions work on ObjectProperties
Simplify EntityList a bit
Remove print statements
Convert URI objects to using TypedFields