Optimize compilation time (#320)

* Print `rerun-if-changed=build.rs` in `build.rs`
* Optimize compile-time: Extract `bin/src/lib.rs`
   
   so that `cargo-binstall (lib)` can be compiled in parallel to other
   deps.
* Refactor: Extract new mod `bin/src/bin_utils.rs`
* Extract new fn `MainExit::new`
* Refactor: Extract new fn `run_tokio_main`
* Handle `Runtime::new` err gracefully in `run_tokio_main`
   instead of `panic!`ing, return the error as `BinstallError`
* Avoid mixing `eprintln` and `error` in `MainExit::report`
* Set profile for `build-override`
   to speedup building of `build.rs` and proc macros.

Signed-off-by: Jiahao XU <Jiahao_XU@outlook.com>

crates/detect-targets/build.rs

@@ -1,4 +1,6 @@
 fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+
     // Fetch build target and define this for the compiler
     println!(
         "cargo:rustc-env=TARGET={}",