rework median - minor changes to std/var

[NRJank]

• median.m: rework matlab compatible function to vectorize code and streamline input processing.
• median.m: simplify calculations by permuting/reshaping all calcs along dim1
• median.m: ensure output type options are consistently handled, clarify option meaning in docstring
• median.m: expand tests, ensure correct operation for corner case inputs (emptys, nan, types, etc.)
• std / var: streamline two vecdim input checks to reduce overhead.

NOTE - early commits make changes to mean that were reverted in late commit. no changes to mean should occur with this PR.