Enabled removing leading comments from json DB (#83)

Encountered a json DB without leading comments.

Added option to adjust the number of expected comments in a json DB.

hippynn/databases/SNAPJson.py

@@ -25,6 +25,7 @@ def __init__(
         transpose_cell=True,
         allow_unfound=False,
         quiet=False,
+        comments=1,
         **kwargs,
     ):
 
@@ -34,6 +35,7 @@ def __init__(
         self.targets = targets
         self.transpose_cell = transpose_cell
         self.depth = depth
+        self.comments = comments
         arr_dict = self.load_arrays(quiet=quiet, allow_unfound=allow_unfound)
 
         super().__init__(arr_dict, inputs, targets, *args, **kwargs, allow_unfound=allow_unfound, quiet=quiet)
@@ -96,7 +98,8 @@ def filter_arrays(self, arr_dict, allow_unfound=False, quiet=False):
 
     def extract_snap_file(self, file):
         with open(file, "rt") as jf:
-            comment = jf.readline()
+            for i in range(self.comments):
+                comment = jf.readline()
             content = jf.read()
         parsed = json.loads(content)
         dataset = parsed["Dataset"]