Stand-alone lesson on plyr
Typos
New example for modeling across sites
Added an intro, expectations and some more examples
Addressing @jdbilshack comments in issue/91
Hard wraps and wrapped long code lines
New example for modeling across sites
Added an intro, expectations and some more examples
Addressing @jdbilshack comments in issue/91
Hard wraps and wrapped long code lines
Changes suggested by @jdblischak
Fixing merge conflicts