add titles and basic todo for sections "package writing", "reproducible research" and "testing"
Revert "add titles and basic todo for sections "package writing", "reproducible research" and "testing""

This reverts commit 8f4d305dcf2c76bc66e3d868556fb1d869e036d0.
Revert "Revert "add titles and basic todo for sections "package writing", "reproducible research" and "testing"""

This reverts commit e4912fa2ad027d4a9df2046f7b7e5be39502af5b.
Merge remote-tracking branch 'origin/master'
spelling change and add TODO for dplyr