Add maxiter parameter to svds.

It is recommended to increase the number of iterations when ARPACK
does not converge
(http://docs.scipy.org/doc/scipy/reference/tutorial/arpack.html).
Add test for svds maxiter keyword.
Add return values for svds.
ENH: sparse.linalg: add more arpack keyword arguments to svds

This adds keyword arguments, apart from the shift-invert mode ones.
More precise docstring for svds.
Added versionadded to new parameters in svds
Merge pull request #376 from fabianp/svds

ENH: sparse.linalg: add arpack keyword parameters to svds()