WIP: Updates to steady state module

Added ARPACK eigensolver, updated power method to use RCM, start from
maximally mixed state, and not recalculate LU factors everytime solver
is called.
changed expm(sparse=...) to expm(method=...) where method can be used to select between qutips and scipys expm functions for sparse/dense matrices.
added unit tests for updated Qobj.expm method
updated comments in Qobj.expm
remove steadystate_nonlinear since it is too experimental still, and not suitable for a release
remove warning that only a single trajectory is ran when collapse operator are not given
quiet the warnings when cython files cannot be deleted (which can happen if they are already deleted, and its not a big deal and warnings is not necessary)
fixed numpy type handling for compability with windows
Merge pull request #184 from jrjohansson/qobj-expm-optionally-dense

Qobj expm optionally dense
Merge pull request #185 from jrjohansson/code-cleanup

Code cleanup
Remove the README.txt for CPC from the repository: only needed for CPC submission, and no need to keep it here
updated changelog in RELEASE.txt
updated url in debian control file
Merge pull request #186 from jrjohansson/3.0-release-updates

minor pre-3.0 release updates
Moved _version2int to utilities module

Also removed _version2tuple
Updated cython files with parameters.pxi file
Added maximally mixed state
made reordering function names more explicit
updated sparse tests with new names
updated steady state solvers and testing functions

- added weighted_bipartite_matching to reordering

- added new eigen solver

-much updated power solver

-combined iterative methods into single function

- dropped support for bicg solver as the new scipy.sparse.linalg docs
suggest that this method works for Hermitian, positive definite
problems only.