Start adding row-level splitting, refactor cli and graph into subcrates

src/bin/cli/main.rs

@@ -0,0 +1,8 @@
+use clap::Parser;
+use coster_rs::cli::Cli;
+
+fn main() -> anyhow::Result<()> {
+    env_logger::init();
+    let cli = Cli::parse();
+    cli.run()
+}