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>
