Hygenic Macros

Requesting Hygenic Macros like in macropy: https://github.com/lihaoyi/macropy

Its useful for example to refer to the columns of a dataframe of object in a formula or expression that is later expanded without being eagerly evaluated :
- `lm(y~x,df)`
- `mutate(flights,
gain = arr_delay - dep_delay,
speed = distance / air_time * 60)`

Or write more complex arbitrary domain specific languages for data analysis packages.

Relevant PEP: https://mail.python.org/pipermail/python-ideas/2015-March/032822.html

More use cases: http://multithreaded.stitchfix.com/blog/2015/03/17/grammar-of-data-science/

CC: @shoyer who might be interested in coconut as a Pydata DSL (with piping, and lots of other functional goodness, compiles to valid python 2/3, 100% compatible with python 3 etc) and this issue specifically.

Thanks!