transmogrify: Add support for NDSize -> PyObject *

Support downgrading of types if all values inside the NDSize
are smaller then max(long)
PyDataArray: Add data_extent property (getter)

Returns a n-tuple where n is the dimensionality of the data and
the the individual elements the size of each dimension
test: Add test for PyDataArray::data_extent property
transmogrify: Add support for PyObject* -> NDSize
PyDataArray: Add data_extent property (setter)
test: Add test for setting PyDataArray::data_extent
Merge pull request #20 from gicmo/data_extent

Add support for DataArray::dataExtent

Verry nice
PyFile: docstrings for File and its mixin
PyDataArray: textual description for data array
test_data_array: fix test with data_extent

array.data_extent = (200, 0) does not work anymore.
(200, ) works, I hope this is correct.
docstrings: move string definitions to *.cpp file

The old version was producing warnigs about unused variables.
PyDataArray: define stubs for binig docstrings
PyDataArray: documentation complete
Merge pull request #22 from stoewer/documentation

Documentation for DataArray

Awesome.
Feature first draft
rebased to the last master
tests for SimpleTag done
tests for the feature added
merged local master