feat: add support for (nearly) any engine (#15)

* feat: add support for (nearly) any engine

* cache response and fixup data depth logic

* use starting slash as non-kv sentinel value

* add tests for custom engines

* improve docs and add descriptor of generic support

* update dist

integrationTests/e2e/e2e.test.js

@@ -6,5 +6,7 @@ describe('e2e', () => {
         expect(process.env.ALTSECRET).toBe("CUSTOMSECRET");
         expect(process.env.NAMED_ALTSECRET).toBe("CUSTOMSECRET");
         expect(process.env.OTHERALTSECRET).toBe("OTHERCUSTOMSECRET");
+        expect(process.env.FOO).toBe("bar");
+        expect(process.env.NAMED_CUBBYSECRET).toBe("zap");
     });
 });