move config loading to config module

This separates concerns a bit more. We will probably want to extend the
logic for config loading in the future, and that stuff should all live
in the relevant place. This change points us in the right direction.

src/config.rs

@@ -1,8 +1,13 @@
-use std::net::{IpAddr, Ipv4Addr};
+use std::{
+    net::{IpAddr, Ipv4Addr},
+    path::Path,
+};
 
 use ruma::{OwnedServerName, RoomVersionId};
 use serde::Deserialize;
 
+use crate::error;
+
 mod proxy;
 
 use proxy::ProxyConfig;
@@ -153,3 +158,20 @@ fn default_turn_ttl() -> u64 {
 pub(crate) fn default_default_room_version() -> RoomVersionId {
     RoomVersionId::V10
 }
+
+/// Load the configuration from the given path
+pub(crate) async fn load<P>(path: P) -> Result<Config, error::Config>
+where
+    P: AsRef<Path>,
+{
+    use error::Config as Error;
+
+    let path = path.as_ref();
+
+    toml::from_str(
+        &tokio::fs::read_to_string(path)
+            .await
+            .map_err(|e| Error::Read(e, path.to_owned()))?,
+    )
+    .map_err(|e| Error::Parse(e, path.to_owned()))
+}