Replace deprecated 'error-chain' with 'thiserror' (#1820)

We can't use #[from] on Error::Msg(String) because String does not implement Error.
(Which it shouldn't; see e.g. https://internals.rust-lang.org/t/impl-error-for-string/8881.)
So we implement From manually for Error::Msg, since our current code was written
in that way for error-chain.

src/bin/bat/app.rs

@@ -62,7 +62,7 @@ impl App {
             // Read arguments from bats config file
             let mut args = get_args_from_env_var()
                 .unwrap_or_else(get_args_from_config_file)
-                .chain_err(|| "Could not parse configuration file")?;
+                .map_err(|_| "Could not parse configuration file")?;
 
             // Put the zero-th CLI argument (program name) first
             args.insert(0, cli_args.next().unwrap());

src/bin/bat/main.rs

@@ -1,6 +1,3 @@
-// `error_chain!` can recurse deeply
-#![recursion_limit = "1024"]
-
 mod app;
 mod assets;
 mod clap_app;