Return sum stats as GRanges or VRanges

[bschilder]

Implemented using new functions to_GRanges and to_VRanges

[bschilder]

Implemented in new function convert_sumstats():

if(return_data){
    message("Returning data directly.")
    out <- convert_sumstats(sumstats_dt = sumstats_return$sumstats_dt, 
                            return_format = return_format)
    return(out)
  } else {
    message("Returning path to saved data.")
    return(check_save_out$save_path) # Returns address of modified file
  }