Re-implement rustbook in terms of mdbook

mdbook has a lot of optional dependencies that we don't want, so instead
of using it directly, we re-build rustbook to use mdbook as a library.
For convenience' sake, we keep the same CLI interface as mdbook; the
only difference is that it only accepts build and test subcommands,
rather than the full range.

src/bootstrap/doc.rs

@@ -47,6 +47,7 @@ pub fn rustbook(build: &Build, target: &str, name: &str) {
     build.run(build.tool_cmd(&compiler, "rustbook")
                    .arg("build")
                    .arg(&src)
+                   .arg("-d")
                    .arg(out));
 }
 

src/doc/book/src/SUMMARY.md

@@ -0,0 +1,3 @@
+# Summary
+
+- [Chapter 1](./chapter_1.md)

src/doc/book/src/chapter_1.md

@@ -0,0 +1 @@
+# Chapter 1

src/doc/nomicon/src/SUMMARY.md

@@ -0,0 +1,3 @@
+# Summary
+
+- [Chapter 1](./chapter_1.md)

src/doc/nomicon/src/chapter_1.md

@@ -0,0 +1 @@
+# Chapter 1

src/tools/rustbook/Cargo.toml

@@ -1,9 +1,12 @@
 [package]
 authors = ["The Rust Project Developers"]
 name = "rustbook"
-version = "0.0.0"
-build = false
+version = "0.1.0"
+license = "MIT/Apache-2.0"
 
-[[bin]]
-name = "rustbook"
-path = "main.rs"
+[dependencies]
+clap = "2.19.3"
+
+[dependencies.mdbook]
+version = "0.0.14"
+default-features = false