[Request] Log Callback API

[gudenau]

Instead of dumping everything into the standard error/out streams or disabling logging all together via env vars (setenv("RUST_LOG", "off", true)).

I propose an API similar to the following:

// Adjust for actual usage in the backing code.
typedef enum {
    WOOTING_LOG_INFO,
    WOOTING_LOG_WARNING,
    WOOTING_LOG_ERROR,
    WOOTING_LOG_FATAL,
} WootingAnalogLogLevel;

typedef void (*WootingAnalogLogFunction)(WootingAnalogLogLevel level, const char* location, const char* message, void* user);

/// Sets the logging callback for the analog SDK. Passing `null` sets the logging backend to the default one.
/// Returns the previous log callback or `null` if none was present.
///
/// This can be called before wooting_analog_initialize,
WootingAnalogLogFunction wooting_analog_log_callback(WootingAnalogLogFunction callback, void* user);

Something similar to this should be fairly flexible but at the same time should not change the existing behavior of the library.

(This is related to #42 but I didn't consider it a duplicate)