Plus42 Equations, Preview Release

[Thomas Okken]

New update:

1. PLOT: When XMIN > XMAX, Bad Things could happen. Added code to sanitize the plot domain and range, to prevent these and other problems.
2. Y^X with complex Y and integer X: removed the repeated-squaring logic, and replaced it with special-case logic for pure-real and pure-imaginary Y and integer X. Other cases are now handled using the logic for complex Y and non-integer real X.