rename overlay_refs to parent_refs... fix up hash string

description..

README.md

@@ -75,7 +75,7 @@ object_marking_refs	Imported from [STIX v2.0 Part 1]: Section 3.1
 granular_markings	Imported from [STIX v2.0 Part 1]: Section 3.1
 hashes		A list of hash strings.
 lang		RFC XXXX language of the properties.
-parent_ref	UUIDv4 of the parent MetaData Object.  Any properties on this object override the parent. (allow deletion via None/null?)  Any missing properties are passed through to the parent for resolution.
+parent_refs	List of UUIDv4s of MetaData Object that overlay.  Any properties on this object override the parent. (allow deletion via None/null?)  Any missing properties are passed through to the parent for resolution.  The first/earliest object that has a property is used in that objects later in the list are "hidden" by the earlier objects.
 mime-type	The mime-type.  If the set of bytes is polymorphic, there should be one for each "type".
 uri		List of URI's where the file may be located.
 child_files	A dictionary where the keys are the file names and the values are hash strings.  (One issue w/ using hashes is that you can't tie YOUR idea of the metadata, but it also allows a person to have metadata about a file that is private and not be forced to share it, nor create a dummy object.)

ui/cli.py

@@ -70,7 +70,7 @@ class MDBase(object):
 	}
 
 	_common_properties = [ 'type', 'created_by_ref' ] # XXX - add lang?
-	_common_optional = set(('overlay_refs', 'sig'))
+	_common_optional = set(('parent_refs', 'sig'))
 	_common_names = set(_common_properties + _generated_properties.keys())
 
 	def __init__(self, obj={}, **kwargs):
@@ -183,7 +183,7 @@ class Identity(MDBase):
 	_common_properties = [ x for x in MDBase._common_properties if x !=
 	    'created_by_ref' ]
 	_common_optional = set([ x for x in MDBase._common_optional if x !=
-	    'overlay_refs' ] + [ 'name', 'pubkey' ])
+	    'parent_refs' ] + [ 'name', 'pubkey' ])
 	_common_names = set(_common_properties + MDBase._generated_properties.keys())
 
 def _trytodict(o):
@@ -363,12 +363,17 @@ class ObjectStore(object):
 
 	@staticmethod
 	def makehash(hashstr, strict=True):
-		'''Take a hash string, and return a valid hash string from it.
+		'''Take a hash or hash string, and return a valid hash
+		string from it.
 
 		This makes sure that it is of the correct type and length.
 
 		If strict is False, the function will detect the length and
-		return a valid hash if one can be found.'''
+		return a valid hash string if one can be found.
+
+		By default, the string must be prepended by the type,
+		followed by a colon, followed by the value in hex in all
+		lower case characters.'''
 
 		try:
 			hash, value = hashstr.split(':')
@@ -759,7 +764,7 @@ class _TestCases(unittest.TestCase):
 			'modified': datetime.datetime(2019, 6, 10, 18, 3, 10),
 			'created_by_ref': self.created_by_ref,
 			'hashes': [ dhash ],
-			'overlay_refs': [ bid ],
+			'parent_refs': [ bid ],
 			'lang': 'en',
 		})
 
@@ -768,7 +773,7 @@ class _TestCases(unittest.TestCase):
 		odict = dict(oobj.items())
 
 		# that is has the overlays property
-		self.assertEqual(odict['overlay_refs'], [ bid ])
+		self.assertEqual(odict['parent_refs'], [ bid ])
 
 		# that it doesn't have a common property
 		self.assertNotIn('type', odict)