Move codespell ignore to a file for easier management (#148)

.codespell_ignore

@@ -0,0 +1,3 @@
+circularly
+copyable
+pullrequest

.pre-commit-config.yaml

@@ -19,7 +19,7 @@ repos:
     rev: v1.17.1
     hooks:
       - id: codespell
-        args: ['-L', 'circularly,copyable,pullrequest']
+        args: ['-I', '.codespell_ignore']
         exclude: '^src/jekyll/Gemfile.lock$'
   - repo: local
     hooks: