add initial help screen + keybinding -> command parsing

still needs some more work, i.e. to show commands in help instead of parsed data
structures, but it's a start.

fixes #117
fixes #121

src/ui/help.rs

@@ -0,0 +1,45 @@
+use std::collections::HashMap;
+
+use cursive::theme::Effect;
+use cursive::utils::markup::StyledString;
+use cursive::view::ViewWrapper;
+use cursive::views::{ScrollView, TextView};
+
+use command::Command;
+use config::config_path;
+use traits::ViewExt;
+
+pub struct HelpView {
+    view: ScrollView<TextView>,
+}
+
+impl HelpView {
+    pub fn new(bindings: HashMap<String, Command>) -> HelpView {
+        let mut text = StyledString::styled("Keybindings\n\n", Effect::Bold);
+
+        let note = format!(
+            "Custom bindings can be set in {} within the [keybindings] section.\n\n",
+            config_path("config.toml").to_str().unwrap_or_default()
+        );
+        text.append(StyledString::styled(note, Effect::Italic));
+
+        let mut keys: Vec<&String> = bindings.keys().collect();
+        keys.sort();
+
+        for key in keys {
+            let command = serde_json::to_string(&bindings[key]).unwrap_or_default();
+            let binding = format!("{} -> {}\n", key, command);
+            text.append(binding);
+        }
+
+        HelpView {
+            view: ScrollView::new(TextView::new(text)),
+        }
+    }
+}
+
+impl ViewWrapper for HelpView {
+    wrap_impl!(self.view: ScrollView<TextView>);
+}
+
+impl ViewExt for HelpView {}

src/ui/mod.rs

@@ -1,6 +1,7 @@
 pub mod album;
 pub mod artist;
 pub mod contextmenu;
+pub mod help;
 pub mod layout;
 pub mod library;
 pub mod listview;