Fix some inconsistencies in the docstring of matrix_rank
Fix some inconsistencies in the docstring of matrix_rank

- Rename the argument from M to A, since M already refers to the number of
  rows in the docstring.

- Fix the documentation for the formula for the default value of tol. It only
  uses the maximum of the number of rows and columns, not the max of all
  dimensions. The code here was correct; only the documentation was wrong.

mhvk/numpy,rgommers/numpy,pdebuyl/numpy,rgommers/numpy,mattip/numpy,mattip/numpy,rgommers/numpy,anntzer/numpy,jakirkham/numpy,anntzer/numpy,seberg/numpy,pdebuyl/numpy,mattip/numpy,seberg/numpy,jakirkham/numpy,mhvk/numpy,mattip/numpy,seberg/numpy,numpy/numpy,jakirkham/numpy,rgommers/numpy,numpy/numpy,numpy/numpy,charris/numpy,mhvk/numpy,jakirkham/numpy,simongibbons/numpy,mhvk/numpy,endolith/numpy,anntzer/numpy,simongibbons/numpy,simongibbons/numpy,endolith/numpy,pdebuyl/numpy,simongibbons/numpy,jakirkham/numpy,seberg/numpy,anntzer/numpy,charris/numpy,charris/numpy,simongibbons/numpy,endolith/numpy,mhvk/numpy,charris/numpy,numpy/numpy,endolith/numpy,pdebuyl/numpy