Add an opt-in option to lowercase filter values

Filter values that only differ in case, like `Mint` and `mint`, came
through as separate values. The new `--lowercase-filters` option
(`lowercase_filters`, `PAGEFIND_LOWERCASE_FILTERS`, and
`lowercaseFilters` / `lowercase_filters` in the Node and Python
wrappers) lowercases filter values when indexing and merges values on
a page that become equal. Filter names are left as they are. Off by
default.

Fixes #737

wrappers/node/types/index.d.ts

@@ -56,6 +56,10 @@ export interface PagefindServiceConfig {
      * @example "<>$"
      */
     includeCharacters?: string,
+    /**
+     * Lowercase filter values when indexing, so that values differing only in case are merged into one.
+     */
+    lowercaseFilters?: boolean,
 }
 
 

wrappers/node/types/internal.d.ts

@@ -34,6 +34,7 @@ export interface InternalPagefindServiceConfig {
     keep_index_url?: boolean,
     write_playground?: boolean,
     include_characters?: string,
+    lowercase_filters?: boolean,
 }
 
 export interface InternalAddFileRequest {