async_std main attribute

Closes #1

Cargo.lock

@@ -36,6 +36,16 @@ version = "0.5.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "23b62fc65de8e4e7f52534fb52b0f3ed04746ae267519eef2a83941e8085068b"
 
+[[package]]
+name = "async-attributes"
+version = "1.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "efd3d156917d94862e779f356c5acae312b08fd3121e792c857d7928c8088423"
+dependencies = [
+ "quote 1.0.8",
+ "syn 1.0.56",
+]
+
 [[package]]
 name = "async-channel"
 version = "1.5.1"
@@ -110,6 +120,7 @@ version = "1.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8f9f84f1280a2b436a2c77c2582602732b6c2f4321d5494d6e799e6c367859a8"
 dependencies = [
+ "async-attributes",
  "async-channel",
  "async-global-executor",
  "async-io",