Macro timespan

macro_rules! timespan {
    ($y:literal y) => { ... };
    ($y:literal years) => { ... };
    ($d:literal d) => { ... };
    ($d:literal days) => { ... };
    ($h:literal : $m:literal : $s:literal) => { ... };
    ($h:literal h) => { ... };
    ($h:literal hrs) => { ... };
    ($h:literal hours) => { ... };
    ($m:literal : $s:literal) => { ... };
    ($m:literal m) => { ... };
    ($m:literal mins) => { ... };
    ($m:literal minutes) => { ... };
    ($s:literal s) => { ... };
    ($s:literal secs) => { ... };
    ($s:literal seconds) => { ... };
    ($(1)?year) => { ... };
    ($(1)?weak) => { ... };
    ($(1)?day) => { ... };
    ($(1)?hour) => { ... };
    ($(1)?hr) => { ... };
    ($(1)?minute) => { ... };
    ($(1)?min) => { ... };
    ($(1)?second) => { ... };
    ($(1)?sec) => { ... };
}

Converts human-readable expression into TimeSpan.