Verbose logging for ReadLoop().

When developing a small IRC bot using go-ircevent, I found it difficult to troubleshoot why I was not getting the expected responses from the server. I added this verbose logging option to help in such situations. It's a boolean member of the Connection struct. When set to true, ReadLoop() will print all raw responses from the server to the standard log.

I also included a small error message text fix in this pull. 

Cheers!
-Ant