pub fn version() -> &'static str {
if cfg!(feature = "v4_10") {
"4.10"
} else if cfg!(feature = "v4_8") {
"4.8"
} else if cfg!(feature = "v4_6") {
"4.6"
} else if cfg!(feature = "v4_4") {
"4.4"
} else if cfg!(feature = "v4_2") {
"4.2"
} else {
"4"
}
}