autotools/configure&make support for build.rs

A build dependency to compile a native library that uses autotools or a compatible configure script + make.

It is based on cmake-rs and the API tries to be as similar as possible to it.

For Emscripten targets like "wasm32-unknown-emscripten", configure and make invocations are passed as arguments to emconfigure and emmake respectively as described in the Emscripten docs.

# Cargo.toml
[build-dependencies]
autotools = "0.2"

// build.rs
use autotools;

// Build the project in the path `foo` and installs it in `$OUT_DIR`
let dst = autotools::build("foo");

// Simply link the library without using pkg-config
println!("cargo:rustc-link-search=native={}", dst.display());
println!("cargo:rustc-link-lib=static=foo");

// build.rs
use autotools::Config;

let dst = Config::new("foo")
    .reconf("-ivf")
    .enable("feature", None)
    .with("dep", None)
    .disable("otherfeature", None)
    .without("otherdep", None)
    .cflag("-Wall")
    .build();