[#293] Add documentation comments and tests for TS Definitions

Notable changes:
- Move index.d.ts from types/ to project root (needed for
  tsd-check module).
- Rename test.ts to index.test-d.ts and place it under root
  (needed for tsd-check module).
- Add tsd-check module to test Typescript Definitions.

Future Work:
The properties inverse, hidden, strikethrough and visible
of Chalk interface in index.d.ts needs to be documented.

package.json

@@ -8,13 +8,13 @@
 		"node": ">=6"
 	},
 	"scripts": {
-		"test": "xo && nyc ava && tsc --project types && flow --max-warnings=0",
+		"test": "xo && nyc ava && tsd-check && flow --max-warnings=0",
 		"bench": "matcha benchmark.js"
 	},
 	"files": [
 		"index.js",
 		"templates.js",
-		"types/index.d.ts",
+		"index.d.ts",
 		"index.js.flow"
 	],
 	"keywords": [
@@ -54,13 +54,15 @@
 		"matcha": "^0.7.0",
 		"nyc": "^13.0.1",
 		"resolve-from": "^4.0.0",
-		"typescript": "^3.0.3",
-		"xo": "^0.23.0"
+		"tsd-check": "^0.2.1",
+		"typescript": "^2.5.3",
+		"xo": "0.20.3"
 	},
 	"types": "types/index.d.ts",
 	"xo": {
 		"ignores": [
-			"test/_flow.js"
+			"test/_flow.js",
+			"*.ts"
 		]
 	}
 }