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DataMatrix variants - EmptyMatrix
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``EmptyMatrix`` is a ``DataMatrix`` variant that does not use a file. Like the name says, it's an empty instance, which only has column names and row names. A typical instantiation of an ``EmptyMatrix`` instance is like this::

	>>> matrix = EmptyMatrix(row_names=["1","2","3"],column_names=["Name","Surname"])

in this case, we create an ``EmptyMatrix`` instance consisting of three rows and two columns. Columns contain only empty lists when the instance is created: we can add column data by using assignments (e.g. ``matrix["Name"] = XXX``) or by inserting or appending rows using the ``append*`` and ``insert*`` methods (which are inherited from ``DataMatrix``).

Aside those details, ``EmptyMatrix`` instances behave exactly like their ``DataMatrix`` equivalents.
