Configure init() to be safe again.

[Anders429]

This removes the unsafe from init() that was added in #8. There are two things to consider here:

1. After further research, it's been determined that the use of the debug registers by other code does not pose a data race, but simply a race condition. Meaning each write to an individual byte cannot be interrupted, and therefore each write cannot be a race. It is still important for this library to ensure log calls disable IME, for the same reasons set forth in Shared global state provides synchronization issues #4, but the fact that this code can overwrite data set by other code is not technically a data race, and therefore not unsafe.
2. This PR disables IME when setting the logger and max level, making those calls safe. This is what all user code should have done after Mark init() as an unsafe function. #8 anyways (and before, since apparently the log initialization functions were likely not working correctly prior to log 0.4.19), so it makes more sense to simply handle it here.