ENH: refactor mio module imports for greater beauty

Remove unused; use bracket instead of backslash continuation.
API: remove use of find_mat_file and deprecate

Deprecate for removal of utility function in next version
API: raise error for >2D array and Mat4 format

Threatened deprecation now an error.
API: make oned_as='row' default for Mat5

Previously `oned_as='column'` was the default; deprecation threatened
for a long time now.
DOC: add io/matlab changes to release notes
RF: remove `find_mat_file`

Discussed on pull request #2704
RF: remove ``oned_as=None`` option and warnings

Remove None as an option to ``oned_as`` and remove associated warnings.
Discussed on pull request 2704
DOC: fix io tutorial for removed deprecations

MATLAB io changed some deprecated defaults; no need to explain this in
the tutorial.

Use `print` less, and use function form of `print`.
Merge pull request #2704 from matthew-brett/remove-matlab-deprecated

MRG: acting on pendng matlab io deprecations