Implement PBKDF

Closes #12

test/pbkdf.test.ts

@@ -0,0 +1,18 @@
+import {expect, test} from 'bun:test'
+
+import {pbkdf} from 'pbkdf'
+
+test('Fields are set correctly', async () => {
+    const pwd = 'password'
+    const salt = new TextEncoder().encode('salt')
+    const usages = ['unwrapKey', 'encrypt']
+
+    const k1 = await pbkdf(pwd, salt, usages)
+    expect(k1.extractable).toBeFalse()
+    expect(k1.type).toBe('secret')
+
+    expect(k1.usages.length).toBe(usages.length)
+    for (const usage of usages) {
+        expect(k1.usages).toContain(usage)
+    }
+})