Use Jekyll.logger instead of Jekyll::Stevenson to log things.
The command-line flags for Jekyll for the source directory and the destination directory are now specified in the docs for the deployment methods.

Fixes #1157.
Use singleton instance variable instead of class variable
Merge pull request #1149 from mojombo/jekyll-logger

Use Jekyll.logger instead of Jekyll::Stevenson to log things
Update history to reflect merge of #1149.