fix(assert): stronger types for equal & is args (#239)

* Connect `actual` and `expects` types in `equal()` and `is()`

* Keep code style

* Simplify types

* Keep origin separations

* Return complex types

src/assert.d.ts

@@ -2,8 +2,10 @@ type Types = 'string' | 'number' | 'boolean' | 'object' | 'undefined' | 'functio
 
 export type Message = string | Error;
 export function ok(actual: any, msg?: Message): asserts actual;
-export function is(actual: any, expects: any, msg?: Message): void;
-export function equal(actual: any, expects: any, msg?: Message): void;
+export function is<Actual, Expects extends Actual>(actual: Actual, expected: Expects, msg?: Message): void;
+export function equal<Actual, Expects extends Actual>(actual: Actual, expected: Expects, msg?: Message): void;
+export function equal<Actual extends Expects, Expects>(actual: Actual, expected: Expects, msg?: Message): void;
+export function equal<Actual, Expects>(actual: Actual, expected: Expects, msg?: Message): void;
 export function type(actual: any, expects: Types, msg?: Message): void;
 export function instance(actual: any, expects: any, msg?: Message): void;
 export function snapshot(actual: string, expects: string, msg?: Message): void;