Add multipart for WASM (#966)

Cargo.toml

@@ -66,6 +66,7 @@ url = "2.1"
 bytes = "0.5"
 serde = "1.0"
 serde_urlencoded = "0.6.1"
+mime_guess = "2.0"
 ## json
 serde_json = { version = "1.0", optional = true }
 
@@ -79,7 +80,6 @@ hyper = { version = "0.13.4", default-features = false, features = ["tcp"] }
 lazy_static = "1.4"
 log = "0.4"
 mime = "0.3.7"
-mime_guess = "2.0"
 percent-encoding = "2.1"
 tokio = { version = "0.2.5", default-features = false, features = ["tcp", "time"] }
 pin-project-lite = "0.1.1"
@@ -141,6 +141,9 @@ features = [
     "RequestMode",
     "Response",
     "Window",
+    "FormData",
+    "Blob",
+    "BlobPropertyBag",
 ]
 
 [[example]]