WIP: Re-implement parser in pest

Parser implementation is kind of iffy. Let's try to re-implement it
using pest.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

Cargo.toml

@@ -6,6 +6,8 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+pest = "2.1"
+pest_derive = "2.1"
 thiserror = "1.0"
 structopt = "0.3"
 regex = "1.5"