Update sampler and add initial R interface

Sampler code in src has been updated and split apart a bit.

An initial test interface for R is under r/

tidying + adding in some extra variables for debugging for now

change scale to rate (1/scale) for gamma distributions

the gamma distribution in R uses shape and /rate/ as its parameters,
whereas gsl_gamma uses shape and scale. so convert to scale to rate in
order to have apples to apples parity with R

'/' -> '+'

readme

Add src and data

update gitignore

Init repo