Move backend checks to build.rs to fail fast, and updated dependencies

build.rs

@@ -1,6 +1,12 @@
 use std::process::Command;
 
 fn main() {
+    #[cfg(all(feature = "sqlite", feature = "mysql"))]
+    compile_error!("Can't enable both backends");
+
+    #[cfg(not(any(feature = "sqlite", feature = "mysql")))]
+    compile_error!("You need to enable one DB backend. To build with previous defaults do: cargo build --features sqlite");
+
     read_git_info().ok();
 }