Adding more options to customize

Hi! In my project I needed ability to set various `extra`/`tags` per message. Thus I've created few new methods for that

```objc
- (void)captureMessage:(NSString *)message
                 level:(RavenLogLevel)level
       additionalExtra:(NSDictionary *)additionalExtra
        additionalTags:(NSDictionary *)additionalTags;

- (void)captureMessage:(NSString *)message
                 level:(RavenLogLevel)level
       additionalExtra:(NSDictionary *)additionalExtra
        additionalTags:(NSDictionary *)additionalTags
                method:(const char *)method
                  file:(const char *)file
                  line:(NSInteger)line;

- (void)captureException:(NSException *)exception
         additionalExtra:(NSDictionary *)additionalExtra
          additionalTags:(NSDictionary *)additionalTags
                 sendNow:(BOOL)sendNow;


```

Also I've added ability to remove default tags, that are set in `setTags:` method

```objc
 (void)setTags:(NSDictionary *)tags withDefaultValues:(BOOL)withDefaultValues;
```