Show more information in console output

[paulrobertlloyd]

Somewhat related to #282, it might be helpful to show more information about the site build in the console output. Possible information that’s currently missing:

• Total time to build site
• What aspects of the build are consuming a high percentage of build time[^1]
• If Lume is out of date
• Other ideas…

[^1]: Worth noting that I’m currently doing some quite awful things with pagination, looping over many different pages and data sources, and Lume hasn’t broken a sweat!

[oscarotero]

When lume is out of date, you should see a warning once per day. Total time to build is a good idea. Aspects of build consuming high percentage of time is more difficult, but it's interesting. I'll think about that.

[oscarotero]

Added the message ${total} files generated in ${duration} seconds.