bloopz_sdk 0.4.0

Bloopz SDK: capture Play Store install referrer and send CPI postbacks.

0.4.0

• Breaking: CPI postback uses POST /api/postback/cpi with JSON body (utm_source, utm_medium, key). BloopzPostback.sendCpi now requires a key argument (provide at runtime; do not hardcode).
• README: document the POST API, curl example, and supplying the key (e.g. String.fromEnvironment).
• Add MIT LICENSE.
• pubspec: add repository metadata for pub.dev.
• pubspec: bump minimum Flutter SDK to >=1.20.0 (required by pub.dev for plugins that don’t ship an ios/ folder).

0.0.1

• Add Android Install Referrer listener (stream + one-shot getter).
• Add utilities to parse utm_source / utm_medium from the referrer.
• Add CPI postback helper for GET /api/postback/cpi.