Add "bundle" type

Not sure *exactly* what this does but i basically just copied the
parts i thought were relevant from the site code. We have a src dir,
which is what needs to be watched, and an output dir, which is what
needs to be analyzed, and a build command, which is what needs to be
run when we wanna run the build.

src/settings/toml/bundle.rs

@@ -0,0 +1,62 @@
+use std::env;
+use std::path::PathBuf;
+use std::process::Command;
+
+use serde::{Deserialize, Serialize};
+
+const OUTPUT_DIR: &str = "dist";
+const SRC_DIR: &str = "src";
+
+#[derive(Clone, Debug, Deserialize, PartialEq, Serialize)]
+#[serde(deny_unknown_fields)]
+pub struct Bundle {
+    #[serde(rename = "build-command")]
+    build_command: Option<String>,
+    #[serde(rename = "output-dir")]
+    output_dir: Option<PathBuf>,
+    #[serde(rename = "src-dir")]
+    src_dir: Option<PathBuf>,
+}
+
+impl Bundle {
+    fn dir_or_default(dir: &Option<PathBuf>, default: &str) -> PathBuf {
+        match dir {
+            Some(path) => path.to_owned(),
+            None => PathBuf::from(default),
+        }
+    }
+
+    pub fn output_dir(&self) -> Result<PathBuf, std::io::Error> {
+        let current_dir = env::current_dir()?;
+        let output_dir = current_dir.join(Bundle::dir_or_default(&self.output_dir, OUTPUT_DIR));
+        Ok(output_dir)
+    }
+
+    pub fn src_dir(&self) -> Result<PathBuf, std::io::Error> {
+        let current_dir = env::current_dir()?;
+        let src_dir = current_dir.join(Bundle::dir_or_default(&self.src_dir, SRC_DIR));
+        Ok(src_dir)
+    }
+
+    pub fn build_command(&self) -> Command {
+        let args_string = match &self.build_command {
+            Some(cmd) => cmd.to_owned(),
+            None => "npm run build".to_string(),
+        };
+        let args: Vec<&str> = args_string.split_whitespace().collect();
+
+        let command = if cfg!(target_os = "windows") {
+            let mut c = Command::new("cmd");
+            c.arg("/C").args(args.as_slice());
+            c
+        } else {
+            let mut c = Command::new(args[0]);
+            if args.len() > 1 {
+                c.args(&args[1..]);
+            }
+            c
+        };
+
+        command
+    }
+}

src/settings/toml/mod.rs

@@ -1,3 +1,4 @@
+mod bundle;
 mod deploy_config;
 mod dev;
 mod environment;
@@ -8,6 +9,7 @@ mod site;
 mod target;
 mod target_type;
 
+pub use bundle::Bundle;
 pub use deploy_config::{DeployConfig, Zoned, Zoneless};
 pub use environment::Environment;
 pub use kv_namespace::{ConfigKvNamespace, KvNamespace};