Oneshot mode and general improved error handling

Cargo.lock

@@ -17,6 +17,12 @@ version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e999941b234f3131b00bc13c22d06e8c5ff726d1b6318ac7eb276997bbb4fef0"
 
+[[package]]
+name = "anyhow"
+version = "1.0.71"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9c7d0618f0e0b7e8ff11427422b64564d5fb0be1940354bfe2e0529b18a9d9b8"
+
 [[package]]
 name = "autocfg"
 version = "1.1.0"
@@ -1133,6 +1139,7 @@ checksum = "d29ab0c6d3fc0ee92fe66e2d99f700eab17a8d57d1c1d3b748380fb20baa78cd"
 name = "screencap-bot"
 version = "0.1.0"
 dependencies = [
+ "anyhow",
  "dotenvy",
  "eggbug",
  "env_logger",