Extended timestamp returns Option<&u32>, which could be copied instead (so Option<u32>)

[zeichenreihe]

Is your feature request related to a problem? Please describe.
So I'm getting the modification times of a file inside a zip file, with the methods here:

zip2/src/extra_fields/extended_timestamp.rs

Lines 73 to 86 in 28fb992

	/// returns the last modification timestamp
	pub fn mod_time(&self) -> Option<&u32> {
	self.mod_time.as_ref()
	}
	/// returns the last access timestamp
	pub fn ac_time(&self) -> Option<&u32> {
	self.ac_time.as_ref()
	}
	/// returns the creation timestamp
	pub fn cr_time(&self) -> Option<&u32> {
	self.cr_time.as_ref()
	}

It's annoying to have to deal with Option<&u32>. In some cases you need to deref it (so something like if let Some(x) = file.ac_time() { let time = *x; ... }), or you need to use .copied() to convert Option<&u32> into Option<u32>.

Describe the solution you'd like
I think it would be better to have this api return Option<u32>, since u32 is easily copyable.
One way would be to have methods like

/// returns the last modification timestamp 
pub fn modification_time(&self) -> Option<u32> { 
    self.mod_time
} 
 
/// returns the last access timestamp 
pub fn access_time(&self) -> Option<u32> { 
    self.ac_time
} 
 
/// returns the creation timestamp 
pub fn creation_time(&self) -> Option<u32> { 
    self.cr_time
}

Describe alternatives you've considered
The alternative to this is to put use x.cr_time().copied(), instead of the proposed x.creation_time().

Another idea would be to have these return some struct encapsulating the fact that it's actually an unix timestamp that's stored here. This struct would look like UnixTimestamp(u32), and would also #[derive(Copy)].

Another idea would be to have a proper time type, from some other crate (chrono?).