Extensions/helpers for serde
```rust
pub struct Foo {
#[serdeext(default(literal = 23))]
a: i32,
#[serdeext(default(inline = r#"|| String::from("Hello") "#))]
b: String,
#[serde(deserializewith = "serdeext::de::parsable")]
url: url::Url,
#[serde(with = "serdeext::base64")]
base64bytes: Vec
fn main() {
println!(
"{:?}",
serde_json::from_str::<Foo>(r#"{
"a": 22,
"bar": "x",
"url": "http://google.com",
"base64_bytes": "aGVsbG8gd29ybGQ=",
"non_empty_string": "a"
}"#)
);
} ```