add a plist macro - copied from serde_json

[aluedeke]

i copied the json macro from serde and modified it i create plist::Value from json annotation. This is super handy when working with lockdown and usbmuxd messages.

I am relatively new to rust, thus i would appreciate any feedback.

The original macro was copied from here: https://github.com/serde-rs/json/blob/c4f24f3be29a3d096d3ac7b1d5594777a613ec0d/src/macros.rs