Adds Tau constant using meval::Context. Also adds a test to match pi's. Note: Tau ends up not being more precise than 2*pi. Resolves: #2258
calc
math eval
* Rename `calc` to `math eval` and allow it to optionally take the expression as an argument * Moved calc tests to math eval Also added 2 tests and changed 1 test * Move calc docs to math eval