Add example Aptos contract (#325)

* Add example Aptos contract

* Remove unneeded dependencies

* Remove comment

aptos/example/Move.toml

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+[package]
+name = "Example Pyth App"
+version = "0.0.1"
+upgrade_policy = "compatible"
+
+[dependencies]
+Pyth = { git = "https://github.com/pyth-network/pyth-crosschain.git", subdir = "aptos/contracts", rev = "main" }
+
+[addresses]
+example = "0xac74082dfffb80824955aaefb2b0a98634b1368e37f42cbff14564ea430b97dc"
+# On deployment, these should be overridden with --named-addresses using the addresses
+# documented at https://docs.pyth.network/consume-data/aptos#addresses
+pyth = "_"
+deployer = "_"
+wormhole = "_"
+
+[dev-addresses]
+pyth = "0xe2f37b8ac45d29d5ea23eb7d16dd3f7a7ab6426f5a998d6c23ecd3ae8d9d29eb"
+deployer = "0x277fa055b6a73c42c0662d5236c65c864ccbf2d4abd21f174a30c8b786eab84b"
+wormhole = "0x251011524cd0f76881f16e7c2d822f0c1c9510bfd2430ba24e1b3d52796df204"

aptos/example/sources/example.move

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+module example::example {
+    use pyth::pyth;
+    use pyth::price::Price;
+    use pyth::price_identifier;
+    use aptos_framework::coin;
+    
+    /// Updates the Pyth price feeds using the given pyth_update_data, and then returns 
+    /// the BTC/USD price.
+    public fun get_btc_usd_price(user: &signer, pyth_update_data: vector<vector<u8>>): Price {
+
+        // First update the Pyth price feeds
+        let coins = coin::withdraw(user, pyth::get_update_fee());
+        pyth::update_price_feeds(pyth_update_data, coins);
+
+        // Price Feed Identifier of BTC/USD in Testnet
+        let btc_price_identifier = x"f9c0172ba10dfa4d19088d94f5bf61d3b54d5bd7483a322a982e1373ee8ea31b";
+
+        // Now we can use the prices which we have just updated
+        let btc_usd_price_id = price_identifier::from_byte_vec(btc_price_identifier);
+        pyth::get_price(btc_usd_price_id)
+
+    }
+}