- Added optional macro arguments using `macro foo(int x = ...)` which can be checked using `$defined(x)`.
- Supplemental `roundeven` has a normal implementation.
* C3_MATH feature
This feature allows the usage of noclib math files even when libc is in use.
If a nolibc symbol exists, it will be used in place of libc, otherwise
it will default to libc.
* Added MIT License notices to atan.c3