Add an 'Add' benchmark
sieve class
Calculate determinant using bareis method
Added setup.py.  python setup.py install now calls cmake and installs
python package csympy
Updated travis tests
Restored old travis tests and added new tests for PYTHON_INSTALL for
2.6, 2.7, 3.2, 3.3, 3.4
Implement berkovitz algorithm
Set flags to do an "intree" build when testing 'python setup.py install'
untabified
overwrite build instead of build_py to ensure shared libraries built by
cmake get copied to proper locations for python install
Added complex `I`.
Remove redundant function declarations and add a description about `berkowitz`
Merge branch 'master' into determinant

Conflicts:
	src/dense_matrix.cpp
	src/matrix.h
	src/tests/matrix/test_matrix.cpp
Fix an important bug (don't steal the dict_)

We can't steal the dict_, because sometimes there is more than one reference to
Mul, so all the other Mul's then become corrupt.

Test was added. We can enable the Python test, as it works now.
Steal the dictionary only for refcount_ == 1

This brings back the optimal speed.
Only access refcount_ in non-thread safe mode

Just to be sure. Add documentation.
Speedup the other branch
Do a copy in pow.cpp rather than move

Because the refcount is not always 1 here.
Refactor the code
Only use refcount_ with WITH_CSYMPY_RCP=yes