[examples] fix pep8 errors E26*

and minor modification of the output of autopep8 where appropriate
[examples] switch to print function everywhere + fix E211

Signed-off-by: Thomas Hisch <t.hisch@gmail.com>
readability improvement in usetex_demo
Merge pull request #3668 from thisch/pep8fix26

[examples] pep8 fix E26*