Add type definitions file

Refs #80

package.json

@@ -4,6 +4,7 @@
   "description": "Format whitespace in a SQL query to make it more readable",
   "license": "MIT",
   "main": "lib/sqlFormatter.js",
+  "types": "src/sqlFormatter.d.ts",
   "bin": {
     "sql-formatter": "./bin/sqlfmt.js"
   },

src/sqlFormatter.d.ts

@@ -0,0 +1,19 @@
+export interface FormatOptions {
+  language?:
+    | 'db2'
+    | 'mariadb'
+    | 'mysql'
+    | 'n1ql'
+    | 'plsql'
+    | 'postgresql'
+    | 'redshift'
+    | 'spark'
+    | 'sql'
+    | 'tsql';
+  params?: { [x: string]: string } | string[];
+  indent?: string;
+  uppercase?: boolean;
+  linesBetweenQueries?: number;
+}
+
+export function format(sql: string, options?: FormatOptions): string;