- Docs: CHANGES clarifications

- Docs: More info on `importLocale` for extensions
- Refactoring: Better type-checking on `canvasRGBA_` (but set correctly by default anyways)
- Build: Remove unused Makefile

docs/tutorials/ExtensionDocs.md

@@ -106,7 +106,8 @@ Both `addLangData`
 and `langReady`
 ([JSDocs]{@link module:svgcanvas.ExtensionInitResponse#langReady})
 are passed objects with an `importLocale` function
-([JSDocs]{@link module:SVGEditor~ImportLocale}) that you can use to
+([JSDocs]{@link module:SVGEditor~ImportLocale}) (as well as
+`init`--see the Basic Format section) that you can use to
 import your own extension locales hosted in the above-mentioned directory.
 
 The `importLocale` function will use the detected locale and detected
@@ -124,6 +125,9 @@ The resolved `Promise` value is expected to adhere to
 [`LocaleStrings`]{@link module:locale.LocaleStrings} (as with SVGEdit's
 global locale files).
 
+One may return a Promise (including by `async`/`await`) waiting for
+`importLocale` to resolve so as to delay further processing until complete.
+
 You could also use your own means to store and retrieve locale data for
 your extension (and
 [`importSetGlobalDefault`]{@link module:importModule.importSetGlobalDefault}