Add config file parsing

Use the `serde` and `toml` crates to handle config file parsing.

src/config.rs

@@ -0,0 +1,47 @@
+use serde::Deserialize;
+
+fn default_host() -> String {
+    "localhost".to_string()
+}
+
+const fn default_port() -> u16 {
+    5432
+}
+
+fn default_name() -> String {
+    "whakarite".to_string()
+}
+
+fn default_user() -> String {
+    "whakarite".to_string()
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(deny_unknown_fields)]
+pub struct Database {
+    /// Host of the database
+    #[serde(default = "default_host")]
+    pub host: String,
+
+    /// Port of the database
+    #[serde(default = "default_port")]
+    pub port: u16,
+
+    /// Name of the database
+    #[serde(default = "default_name")]
+    pub name: String,
+
+    /// Name of the user to connect to the database
+    #[serde(default = "default_user")]
+    pub user: String,
+
+    /// Password of the user to connect to the database
+    pub pass: String,
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(deny_unknown_fields)]
+pub struct Config {
+    /// Database configuration
+    pub database: Database,
+}