[params] fix default import

params.py

@@ -39,5 +39,7 @@ def default_params():
 def load_params(filename):
     basic_params = default_params()
     new_params = params_from_file(filename)
-    basic_params.update(new_params)
+    for key in new_params:
+        if key in basic_params:
+            basic_params[key].update(new_params[key])
     return basic_params

params.yml

@@ -11,6 +11,7 @@ plot : # Plot parameters
     time_fmt     :  "time = {:.3g} {}"   # Time format string, 1st field is time and 2nd is unit
 
 rcParams: # Anything there will be passed to matplotlib's rcParams
+   {} # remove and replace by rcParams keys
 
 disk: # Disk speficic parameters
     enable    : False                 # Enable specific disk analysis