chore: rename filters to snake style, #487

BREAKING CHANGE: keys in `<liquidjs>.filters` are now in snake case (instead of camel case), identical to that in Liquid template.

.eslintrc.json

@@ -37,6 +37,11 @@
     "@typescript-eslint/no-unused-vars": ["error", { "vars": "all", "args": "none", "ignoreRestSiblings": false }]
   },
   "overrides": [{
+    "files": ["**/filters/*.ts"],
+    "rules": {
+      "camelcase": "off"
+    }
+  }, {
     "files": ["**/*.js", "**/*.mjs"],
     "rules": {
       "@typescript-eslint/no-var-requires": "off"