Fix toml problem and release 0.0.23

The toml crate removed its serde dependency in 0.3, but in 0.4, it
went away. Cargo didn't warn on this, but now it does. As such, we
need a release so that rust's build doesn't warn constantly.

Author: steveklabnik

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mdbook"
-version = "0.0.22-pre"
+version = "0.0.23"
 authors = ["Mathieu David <[email protected]>"]
 description = "create books from markdown files (like Gitbook)"
 documentation = "http://azerupi.github.io/mdBook/index.html"
@@ -25,7 +25,7 @@ pulldown-cmark = "0.0.14"
 lazy_static = "0.2"
 log = "0.3"
 env_logger = "0.4.0"
-toml = { version = "0.4", features = ["serde"] }
+toml = "0.4"
 open = "1.1"
 regex = "0.2.1"
 tempdir = "0.3.4"