Add From impls for Plist
Add From impls for Plist

Add the most common/reasonable conversions from primitive and std types to Plist
variants. There's a bit of uncertainty with `Vec<u8>` and `&[u8]` where it's not
obvious whether they should convert to `Plist::Array` or `Plist::Data`. I've opted
for `Plist::Data`, but converting to `Plist::Array` would also be reasonable.

ebarnard/rust-plist