Squashed commit of the following:

commit 5eb515f666bfa1ff06c2e96bdc351a4b7456580e
Author: Andrew Senetar <arsenetar@gmail.com>
Date:   Sun Mar 27 22:19:39 2022 -0500

    Add fallback to md5 if xxhash not available

    Mainly here for the case when distributions have not packaged python3-xxhash.

commit 51b18d4c84
Author: Andrew Senetar <arsenetar@gmail.com>
Date:   Sat Mar 19 15:25:46 2022 -0500

    Switch file hashing to xxhash instead of md5

    - Improves performance significantly in some cases
    - Add xxhash to requirements.txt and sort requirements
    - Rename md5 based members to digest
    - Update all tests to use new member names and hashing methods
    - Update hash db code to upgrade schema

    NOTE: May consider supporting multiple hashing algorithms in the future.

core/tests/base.py

@@ -86,9 +86,9 @@ class NamedObject:
             folder = "basepath"
         self._folder = Path(folder)
         self.size = size
-        self.md5partial = name
-        self.md5 = name
-        self.md5samples = name
+        self.digest_partial = name
+        self.digest = name
+        self.digest_samples = name
         if with_words:
             self.words = getwords(name)
         self.is_ref = False