Add TypeScript type definitions (#47)

This way the project can be consumed in TypeScript projects.

Author: remcohaszing

lib/safe-parse.d.ts

@@ -0,0 +1,9 @@
+import type { Parser } from 'postcss'
+
+/**
+ * A fault-tolerant CSS parser for [PostCSS], which will find & fix syntax
+ * errors, capable of parsing any input.
+ */
+declare const safe: Parser
+
+export = safe