More detailed logging upon failure(s)

[ChrisCates]

trafficstars

Sometimes the network can fail or other things can happen... However, we don't have detailed logs for when a failure happens for a specific wet file... Would be nice to have detail logs in the output:

• [x] Better logging for extract.go

• [ ] Better logging for analyze.go

[LastPossum]

For more detailed logging I suggest to:

1. replace CURL and gunzip calls with go code;
2. return error values instead of books;
3. move logging to higher level functions.

I made a pr #3 illustrating this ideas in code

[ChrisCates]

@LastPossum thank you for the pull request. It has been merged... I will look into using more idiomatic error outputs when I do another push.