- `-fsanitize=undefined` encompasses multiple checks we were specifying
- "detect_leaks=1" for `__asan_default_options` checks for memory leaks
(except for with macOS clang++, which does not support LSan)
- `-fsanitize=float-divide-by-zero` is an extra UBSan check
(and reveals a UB bug to fix with fixed-point `DIV` and `LOG`)
- Fixed-point formulas are implemented using IEEE-754 floating-point
internally, which could give infinity or NaN values whose conversion
to fixed-point integer was platform-dependent.
- Formatting fixed-point $8000_0000 (INT32_MIN, -2147483648) was
not putting the negative sign in front.
In exponent(), 'base *= base;' should not run
when base is 65536, since it overflows an int32_t.
This also optimizes exponent() based on
gcc and clang -O3 test cases in godbolt.org.
Document the existing `ROUND`, `CEIL`, and `FLOOR` functions
Also update the trig function docs for searchability
Implement `POW` and `LOG`
Addresses part of #675
Implement ** for integer exponents
** has higher precedence than -, like Python, so -3**4 == -(3**4) == 81
