Add reflective boundary conditions

This MR generalises the periodic boundary conditions to allow reflective boundary conditions.

WIP because I only made it work with dynesty in the first case. Hopefully, this will help sample to the edges of priors for zenith angles.

bilby/core/sampler/dynesty.py

@@ -438,14 +438,8 @@ class Dynesty(NestedSampler):
         The logic ensures that when theta < 0 you shift to |theta| and when
         theta > 1 you return 2 - theta
         """
-        theta_init = theta.copy()
         theta[self._periodic] = np.mod(theta[self._periodic], 1)
         theta_ref = theta[self._reflective]
         theta[self._reflective] = np.minimum(
             np.maximum(theta_ref, abs(theta_ref)), 2 - theta_ref)
-        # theta_ref[theta_ref < 0] = abs(theta_ref[theta_ref < 0])
-        # theta_ref[theta_ref > 1] = 2 - theta_ref[theta_ref > 1]
-        # theta[self._reflective] = theta_ref
-        if min(theta) < 0 or max(theta) > 1:
-            import IPython; IPython.embed()
         return self.priors.rescale(self._search_parameter_keys, theta)