Drawj2d 0.7.1 released

This release improves the math expression evaluator.

Changes:
- command expr enhanced: max and min functions take variable number of arguments. E.g. [expr max(0, 2.0, 4.0, 2.3)]
- command expr enhanced: scientific notation. E.g. "1.2e-5"
- command assert enhanced: approximately equal comparison. E.g. assert "$a ~= $b"
- command expr enhanced: precision increased to 16 digits
- command expr enhanced: new function exp(n) for e^n
- command expr enhanced: expression validation improved