Add a "host" crate for autodetecting the host. (#159)

* Add a "native" crate for autodetecting the host.

* Remove the redundant .gitignore.

* Use the proper builder for enabling subtarget flags.

lib/native/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "cretonne-native"
+version = "0.0.0"
+authors = ["The Cretonne Project Developers"]
+publish = false
+description = "Support for targetting the host with Cretonne"
+repository = "https://github.com/stoklund/cretonne"
+license = "Apache-2.0"
+
+[lib]
+name = "cton_native"
+
+[dependencies]
+cretonne = { path = "../cretonne" }
+
+[target.'cfg(any(target_arch = "x86", target_arch = "x86_64"))'.dependencies]
+raw-cpuid = "3.0.0"