php: fetch: prices: new functionality / refactor

- Add support for multiple aggregator APIs
- Refactor `prices` API implementation
- Update documentation

container/src/finance/lib/internal/fetch/fetch.php

@@ -63,7 +63,9 @@ namespace docker_finance
         $env->set_env('API_OUT_DIR', getenv('API_OUT_DIR') . '/');  // API output path (account's 1-in dir)
 
         // Prices
-        $env->set_env('API_PRICES_PATH', getenv('API_PRICES_PATH'));        // Master file
+        $env->set_env('API_PRICES_PATH', getenv('API_PRICES_PATH'));  // Master price file
+        $env->set_env('API_PRICES_API', getenv('API_PRICES_API'));    // Price API to use
+        $env->set_env('API_PRICES_KEY', getenv('API_PRICES_KEY'));    // Price API key
         $env->set_env('API_PRICES_SYMBOLS', getenv('API_PRICES_SYMBOLS'));  // User-provided symbols
 
         // Exchanges
@@ -104,11 +106,11 @@ namespace docker_finance
                 }
                 break;
             case 'prices':
-                switch ($env->get_env('API_FETCH_SUBTYPE')) {
+                switch ($subtype) {
                     case 'crypto':
+                        // TODO: `case 'legacy'` (stocks and bonds and ETFs, oh my!)
                         $api = new prices\Fetch($env);
                         break;
-                        // TODO: stocks and bonds and ETFs, oh my!
                     default:
                         utils\CLI::throw_fatal("unsupported subtype '$subtype' for interal API");
                         break;