maint/dev ~ add TypeScript dev deps

package.json

@@ -85,6 +85,11 @@
 	"dependencies": {},
 	"devDependencies:#": "* for testing, Node-v6 requires ava < v2 and nyc < v15",
 	"devDependencies": {
+		"@ava/typescript": "^1.1.1",
+		"@istanbuljs/nyc-config-typescript": "^1.0.1",
+		"@types/node": "^14.14.14",
+		"@typescript-eslint/eslint-plugin": "^4.0.1",
+		"@typescript-eslint/parser": "^4.0.1",
 		"ava": "^1.4.1",
 		"codecov": "^3.5.0",
 		"command-exists": "^1.2.9",
@@ -95,14 +100,16 @@
 		"eslint": "^7.11.0",
 		"eslint-config-prettier": "^6.11.0",
 		"eslint-plugin-eslint-comments": "^3.2.0",
+		"eslint-plugin-functional": "^3.0.2",
 		"eslint-plugin-import": "^2.22.0",
 		"is-ci": "^2.0.0",
 		"is-node-modern": "^1.0.0",
 		"npm-run-all": "^4.1.5",
 		"nyc": "^14.1.1",
 		"open-cli": "^6.0.1",
 		"prettier": "^2.1.1",
-		"tsd": "^0.13.1"
+		"tsd": "^0.13.1",
+		"typescript": "^4.0.2"
 	},
 	"optionalDependencies": {},
 	"prettier # overrides/[*.markdown]/tabWidth": "// set to 4 when https://github.com/prettier/prettier/issues/5019 is fixed",