feat: remove "tslib"

This can be done because the minimal required nodejs version is 12.22,
which fully supports async-await, generators and async-generators

though for typescript to apply this it has to be set to es2018, even though
these features are es2016

BREAKING CHANGE:
Typescript "target" is now "es2018", which is a breaking change, but should not affect anything
as long as the required nodejs version is used (12.22 or higher)

package.json

@@ -60,8 +60,7 @@
     "typescript": "~4.4.4"
   },
   "dependencies": {
-    "debug": "^4.3.4",
-    "tslib": "^2.4.0"
+    "debug": "^4.3.4"
   },
   "publishConfig": {
     "access": "public"

tsconfig.json

@@ -1,6 +1,6 @@
 {
   "compilerOptions": {
-    "target": "es6",
+    "target": "ES2018",
     "lib": [
       "esnext"
     ],
@@ -14,7 +14,7 @@
     "allowJs": false,
     "outDir": "build",
     "inlineSourceMap": true,
-    "importHelpers": true,
+    "importHelpers": false,
     "strictBindCallApply": true,
     "strictFunctionTypes": true,
     "strictNullChecks": true