Merge pull request #3997 from juliantaylor/release-notes

DOC: add 1.7.2 release notes
MAINT: Don't use 'import *' in lib/test_twodim_base.py.
ENH: lib: Rewrite vander: make it faster, and add an option to specify the order of the powers (either decreasing or increasing).
MAINT: lib: remove unused imports and PEP8 clean up in twodim_base.py
MAINT: lib: Add a 'See Also' section to the vander docstring, and make a few more PEP8 tweaks.
MAINT: lib: Use a consistent PEP8-compliant import style in twodim_base.py and tests/test_twodim_base.py.  Also make a couple more PEP8 tweaks.
Merge pull request #3999 from WarrenWeckesser/vander

ENH: lib: Rewrite vander
DOC: update 1.7.2 release notes

add two additional fixed bugs