cleanup our type definitions

this fixes one inconsistency with the .d.ts
(focus & blur return the BaseMathQuill rather than void)

this also gets rid of some deduplication by making EditableMathQuill extend
BaseMathQuill, to match the structure of publicapi.ts

src/mathquill.d.ts

@@ -22,45 +22,27 @@ declare namespace MathQuill {
     interface BaseMathQuill {
       id: number;
       data: { [key: string]: any };
-      config(opts: Config): BaseMathQuill;
+      config<T extends BaseMathQuill>(opts: Config): T;
       revert: () => HTMLElement;
-      latex(latex: string): BaseMathQuill;
+      latex<T extends BaseMathQuill>(latex: string): T;
       latex(): string;
       reflow: () => void;
       el: () => HTMLElement;
       getAriaLabel(): string;
-      setAriaLabel(str: string): BaseMathQuill;
+      setAriaLabel<T extends BaseMathQuill>(str: string): T;
       html: () => string;
       mathspeak: () => string;
       text(): string;
-      blur: () => void;
-      focus: () => void;
+      blur<T extends BaseMathQuill>(): T;
+      focus<T extends BaseMathQuill>(): T;
       selection(): {
         latex: string;
         startIndex: number;
         endIndex: number;
       };
     }
 
-    interface EditableMathQuill {
-      id: number;
-      data: { [key: string]: any };
-      revert: () => HTMLElement;
-      config(opts: Config): EditableMathQuill;
-      latex(latex: string): EditableMathQuill;
-      latex(): string;
-      reflow: () => void;
-      el: () => HTMLElement;
-      getAriaLabel(): string;
-      setAriaLabel(str: string): EditableMathQuill;
-      html: () => string;
-      mathspeak: () => string;
-      text(): string;
-      selection(): {
-        latex: string;
-        startIndex: number;
-        endIndex: number;
-      };
+    interface EditableMathQuill extends BaseMathQuill {
       select: () => EditableMathQuill;
       moveToRightEnd: () => EditableMathQuill;
       moveToLeftEnd: () => EditableMathQuill;
@@ -69,8 +51,6 @@ declare namespace MathQuill {
       keystroke: (key: string, evt?: KeyboardEvent) => EditableMathQuill;
       typedText: (text: string) => EditableMathQuill;
       clearSelection: () => EditableMathQuill;
-      blur: () => EditableMathQuill;
-      focus: () => EditableMathQuill;
       getAriaPostLabel: () => string;
       setAriaPostLabel: (str: string, timeout?: number) => EditableMathQuill;
       ignoreNextMousedown: (func: () => boolean) => EditableMathQuill;