Transformation structures into a dict and backwards
===================================================
E.g. transfirmation structures into a dict is used
for passing structures to **pickle**...

to_dict(structure)
~~~~~~~~~~~~~~~~~~
The function creates a dict with structure's contents. It works recursively. 

 >>> from structures import *
 >>> class S(Structure):
 ...     class s(Structure):
 ...         i = Integer(13)
 ...     f = Float(3.14)
 ...     l = List([1, set([2, 3])])
 ...
 >>> s = S()
 >>> assert to_dict(s) == {'s': {'i': 13}, 'f': 3.14, 'l': [1, set([2, 3])]}


from_dict(structure_class, data)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The function creates structure **structure_class** from the dict **data**.
It creates substructures appropriate types too i.e. it works recursively.

 >>> from structures import *
 >>> class S(Structure):
 ...     class s(Structure):
 ...         i = Integer(13)
 ...     f = Float(3.14)
 ...     d = Decimal('8.62')
 ...
 >>> s = from_dict(S, {'s': {'i': 26}, 'd': '2.64', 'f': 9.82})
 >>> assert s.f == 9.82
 >>> assert s.s.i == 26
 >>> s.d
 Decimal('2.64')