Pyreadr

* fixing seg fault with linux wheels 62

* Implemented reading dataframe rownames as pandas index
* Implementing reading matrices, arrays, tables, solves 5.
* librdata source updated to commit 8623be2c626392028cd75c5fc45a90e1f70d97b9

* Fixed sharing flags for opening files on windows

* Added download\_file function
* using std=gnu99 from env_vars.sh in wheels to solve 56

* Added license to setup.py

* Solved 48