message: Insert a basic Cargo.toml if one is not defined.
diff: @@ -11,7 +11,6 @@ specify some files to create. The general form looks like this:
  ```
  let p = project()
  - .file("Cargo.toml", &basic_bin_manifest("foo"))
  .file("src/main.rs", r#"fn main() { println!("hi!"); }"#)
  .build();
  ```
  @@ -119,6 +118,13 @@ pub mod paths;
  pub mod publish;
  pub mod registry;
  +const BASIC_MANIFEST: &str = r#"
  +[package]
  +name = "foo"
  +version = "0.0.1"
  +authors = []
  +"#;
  +
  /*
  *
  * ===== Builders =====
  @@ -243,13 +249,18 @@ impl ProjectBuilder {
  }
  /// Create the project.
  - pub fn build(self) -> Project {
  + pub fn build(mut self) -> Project {
  // First, clean the directory if it already exists
  self.rm_root();
  // Create the empty directory
  self.root.root().mkdir_p();
  + let manifest_path = self.root.root().join("Cargo.toml");
  + if self.files.iter().all(|fb| fb.path != manifest_path) {
  + self._file(Path::new("Cargo.toml"), BASIC_MANIFEST)
  + }
  +
  for file in self.files.iter() {
  file.mk();
  }
  