Update README.md

Add test.py usage.

Update thanks section.
[Calc] Fix issue FS#278. Some variables coudn't be modified.

Variables which names started with a keyword (del, def, if, else...)
always returned `None`.
For example, executing `delta = 25` would have no effect.
Merge branch 'master' of github.com:wxgeo/geophar into geophar