Enable inheritance from HappyMapper classes

This is convenient if an XSD contains inheritance relationships. Can
also be used for multiple (top-level) elements that share the same type.
The subclass will inherit all attributes, elements, etc. from the
superclass and can add to them, independent of the superclass.
Cleaned whitespace
item#typecast

The typecast methods now more flexible and you can define additional
typecasting typecasters without adding to the same method.
Merge pull request #27 from Confusion/inheritance-support

Enable inheritance from HappyMapper classes
fixed default namespaces
Refactored HappyMapper#find

Split HappyMapper#find into three separate methods in the three separate
nodes types. This obviates the need for the #attribute?, #element? and
 #text_node?
More documentation about types conversion
Removed the un-needed block for NilOrAlreadyConverted
Removed Types and #primitive_type method
Clean up paths in #from_xml_node for types and xml content
Custom Parser and Default Parser in methods
Minor refactor to #constantize
keeps Boolean out of global namespace
whitespace nits
Merge pull request #35 from haarts/master

Puts top level Boolean class in module HappyMapper
Spec - cleaned up unused creation in Attribute Spec
Merge branch 'refactor-typecast'

Conflicts:
	lib/happymapper/item.rb
Merge branch 'refactor-from_xml_node'
FIX the requires
Moved 'version' into the happymapper dir like most sane gems