Eliminate subcycles and photons_per_cycle variable in favour of NPHOT

In #114 I discussed eliminating subcycles.

This is done here. The loop over subcycles has been removed, as has the code that assigned photons_per_cycle. NPHOT is now the only variable which contains photons_per_cycle. 

This also involved changing the following section, in which j was the subcycle iteration counter:

```C 
	  if (!geo.wind_radiation || (geo.wcycle == 0 && geo.wind_type != 2))
	    iwind = -1;		/* Do not generate photons from wind */
	  else if (j == 0)
	    iwind = 1;		/* Create wind photons and force a reinitialization of wind parms */
	  else
	    iwind = 0;		/* Create wind photons but do not force reinitialization */
```

To

```C 
	  if (!geo.wind_radiation || (geo.wcycle == 0 && geo.wind_type != 2))
	    iwind = -1;		/* Do not generate photons from wind */
	  else
	    iwind = 1;		/* Create wind photons and force a reinitialization of wind parms */
```

Which I think is correct, and is certainly the old behaviour as j was always 0 in recent ish models. We want create wind photons and force a reinitialization every cycle except the first, right?