Various unimportant minor style/doc fixups

Signed-off-by: Manos Pitsidianakis <manos@pitsidianak.is>

meli/src/accounts.rs

@@ -830,9 +830,10 @@ impl Account {
         ret
     }
 
-    pub fn mailboxes_order(&self) -> &Vec<MailboxHash> {
+    pub fn mailboxes_order(&self) -> &[MailboxHash] {
         &self.mailboxes_order
     }
+
     pub fn name(&self) -> &str {
         &self.name
     }

meli/src/conf.rs

@@ -165,7 +165,7 @@ pub struct FileAccount {
     pub identity: String,
     #[serde(default)]
     pub extra_identities: Vec<String>,
-    #[serde(default = "none")]
+    #[serde(default = "none", skip_serializing_if = "Option::is_none")]
     pub display_name: Option<String>,
 
     #[serde(default = "false_val")]
@@ -180,14 +180,18 @@ pub struct FileAccount {
     pub order: (SortField, SortOrder),
     #[serde(default = "false_val")]
     pub manual_refresh: bool,
-    #[serde(default = "none")]
+    #[serde(default = "none", skip_serializing_if = "Option::is_none")]
     pub refresh_command: Option<String>,
     #[serde(flatten)]
     pub conf_override: MailUIConf,
     #[serde(flatten)]
-    #[serde(deserialize_with = "extra_settings")]
-    pub extra: IndexMap<String, String>, /* use custom deserializer to convert any given value
-                                          * (eg bool, number, etc) to string */
+    #[serde(
+        deserialize_with = "extra_settings",
+        skip_serializing_if = "IndexMap::is_empty"
+    )]
+    /// Use custom deserializer to convert any given value (eg `bool`, number,
+    /// etc) to `String`.
+    pub extra: IndexMap<String, String>,
 }
 
 impl FileAccount {
@@ -195,10 +199,6 @@ impl FileAccount {
         &self.mailboxes
     }
 
-    pub fn mailbox(&self) -> &str {
-        &self.root_mailbox
-    }
-
     pub fn search_backend(&self) -> &SearchBackend {
         &self.search_backend
     }

melib/src/conf.rs

@@ -33,6 +33,10 @@ pub use crate::{SortField, SortOrder};
 #[derive(Clone, Debug, Default, Serialize)]
 pub struct AccountSettings {
     pub name: String,
+    /// Name of mailbox that is the root of the mailbox hierarchy.
+    ///
+    /// Note that this may have special or no meaning depending on the e-mail
+    /// backend.
     pub root_mailbox: String,
     pub format: String,
     pub identity: String,