Minor adjust to the ROQ weight generation

1. Convert the light travel time explicitly calculated value: uses 1.1 * R_earth / c (i.e. 10% more than the expected maximum)
2. Use a single fixed time_space: previously, the time resolution was set, then recalculated from the difference in the first two elements of time_samples. This could lead to buggy behaviour since that is no longer an evenly spaced array after the subtraction from the start time is made.
3. Add info statements
4. Adds a check if the seglen is shorter than the duration
5. Apply a safety factor of 5 to ensure the time step is short enough. This will increase the size of the ROQ array basis by ~ a factor of 5, but in testing I found it helped remove bias from examples just searching over RA, DEC, and geocent_time.
6. Add explicit clean up of memory

Closes #372 (closed)

bilby/gw/likelihood.py

@@ -925,7 +925,8 @@ class ROQGravitationalWaveTransient(GravitationalWaveTransient):
 
         """
 
-        earth_light_crossing_time = 2 * radius_of_earth / speed_of_light
+        # Maximum delay time to geocentre plus 10%
+        earth_light_crossing_time = 1.1 * radius_of_earth / speed_of_light
         time_space = self._get_time_resolution()
         delta_times = np.arange(
             self.priors['geocent_time'].minimum - earth_light_crossing_time,