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

@@ -17,8 +17,7 @@ from scipy.special import i0e
 from ..core import likelihood
 from ..core.utils import (
     logger, UnsortedInterp2d, BilbyJsonEncoder, decode_bilby_json,
-    create_frequency_series, create_time_series, speed_of_light,
-    radius_of_earth)
+    create_time_series, speed_of_light, radius_of_earth)
 from ..core.prior import Interped, Prior, Uniform
 from .detector import InterferometerList
 from .prior import BBHPriorDict