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rm flattr

Merge pull request #4 from jtsay362/master

Be a bit more lenient when calculating scale, so we don't mess up the gridlines

Restore lint fixes

Replace parser with math.js which supports more functions and accepts more syntax

Merge pull request #3 from jtsay362/master

Optimize calculations by reusing parsed expressions.

Fix lint warnings

Support more functions: gamma, zeta, fact, bellb, csc, sec, cot

Code cleanup; added jsgcalc.drawFillArea

Update README.md

Fix derivatives (again)