Downsample before applying conversion function

The purpose of this MR is to apply the downsampling before applying the conversion function. This will then reduce overall runtime for large result files. This fixes issue #205 (closed).

pesummary/gw/file/formats/pesummary.py

@@ -135,6 +135,8 @@ class PESummary(GWRead, CorePESummary):
         data = self.load_from_function(
             function, self.path_to_results_file, **kwargs)
         self.data = data
+        self.parameters = self.data["parameters"]
+        self.samples = self.data["samples"]
         if "mcmc_samples" in data.keys():
             self.mcmc_samples = data["mcmc_samples"]
         if "version" in data.keys() and data["version"] is not None: