mod(structure): update project structure

Remove examples, add description for design goals in README.md and
apply re-names and naming changes accordingly for the project structure.
Implement a flat hierachry, as the library shall remain pretty simple.

src/event.zig

@@ -3,26 +3,31 @@
 const std = @import("std");
 const terminal = @import("terminal.zig");
 
-const Size = terminal.Size;
-const Key = terminal.Key;
-
-pub const Error = struct {
-    err: anyerror,
-    msg: []const u8,
-};
+const Size = @import("size.zig");
+const Key = @import("key.zig");
 
 // System events available to every application.
-// TODO: should this also already include the .view enum option?
 pub const SystemEvent = union(enum) {
+    /// Initialize event, which is send once at the beginning of the event loop and before the first render loop
+    init,
+    /// Quit event to signify the end of the event loop (rendering should stop afterwards)
     quit,
-    err: Error,
+    /// Error event to notify other containers about a recoverable error
+    err: struct {
+        err: anyerror,
+        /// associated error message
+        msg: []const u8,
+    },
+    /// Resize event emitted by the terminal to derive the `Size` of the current terminal the application is rendered in
     resize: Size,
+    /// Input key event received from the user
     key: Key,
+    /// Focus event for mouse interaction
+    /// TODO: this should instead be a union with a `Size` to derive which container / element the focus meant for
     focus: bool,
 };
 
 pub fn mergeTaggedUnions(comptime A: type, comptime B: type) type {
-    // TODO: should this expect one of the unions to contain the .view value option with its corresponding associated type?
     if (!isTaggedUnion(A) or !isTaggedUnion(B)) {
         @compileError("Both types for merging tagged unions need to be of type `union(enum)`.");
     }