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
With permission from the main authors [1], most of the code has been
relicensed under the MIT license.
SPDX license identifiers are used so that the license headers in source
code files aren't too large.
Add CONTRIBUTORS.rst file.
[1] https://github.com/rednex/rgbds/issues/128
Signed-off-by: Antonio Niño Díaz <antonio_nd@outlook.com>
