Initial thoughts/expt
New way to create functions.
Flexible way to specify functions
Move funs to own file and cleanup
New strategy (and name) for colwise_q
Cleaner standard & non-standard evaluation forms
Capture environment in funs
Better names for calls
summarise_each and mutate_each
Improve docs for summarise_each/mutate_each
Make standard eval version of select_vars
Use name preserving version of setdiff
Export summarise_each
Add note in news. Closes #178