Allow requesting badges for branches != master

This changed the cache structure to allow caching data for multiple
branches. The service still assumes a default branch named `master` but
using the `branch` get parameter, the default branch can be changed.

The 404 page for the missing `master` branch was changed to explain the
new parameter.

src/config.rs

@@ -50,7 +50,6 @@ pub(crate) struct Opt {
 
 pub(crate) async fn init() -> Result<()> {
     std::env::set_var("RUST_LOG", "actix_web=info,hoc=info");
-    // pretty_env_logger::init();
     openssl_probe::init_ssl_cert_env_vars();
     let stdout = ConsoleAppender::builder().build();
     let file = FileAppender::builder()