calc_rad_loss(): aded call to check_download_file() to ensure chianti_rad_loss.csv exists locally on user's machine.  This also required added download_dir kwarg to calc_rad_loss() and rad_loss_rate().
calc_rad_loss(): aded call to check_download_file() to ensure
chianti_rad_loss.csv exists locally on user's machine.  This also
required added download_dir kwarg to calc_rad_loss() and rad_loss_rate().

dpshelio/sunpy,dpshelio/sunpy,Alex-Ian-Hamilton/sunpy,Alex-Ian-Hamilton/sunpy,Alex-Ian-Hamilton/sunpy,dpshelio/sunpy