Improvements (#33)

1. Skip recording undefined variables
2. Parse `in` correctly if it is not imported.
3. base64.decode
4. Handle `with` modifier for qualified data and input.

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

Cargo.toml

@@ -14,6 +14,7 @@ log = "0.4.17"
 env_logger="0.10.0"
 lazy_static = "1.4.0"
 rand = "0.8.5"
+data-encoding = "2.4.0"
 
 [dev-dependencies]
 clap = { version = "4.4.7", features = ["derive"] }