Initial version of single binary hot-reloading

docs/hot-reloading.md

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+# Hot Reloading
+
+Instead of having the engine as an exe and game as a dll, and having to jump
+through hoops to share libraries internal state between them we do it
+differently. The engine and game live in the same binary, compiled fully each
+time. We rely mostly on static memory, and register these memory regions. Then
+when we want to hot reload: we send a close signal to the running instance, it
+writes a snapshot of the active memory to disk, instance closes, recompile,
+restart the application, it restores the memory from the snapshot.
+
+## Byte Layout On Disk
+
+```odin
+Snapshot_Header :: struct #packed #all_or_none {
+	magic_string:     u32,
+	version:          u16, // spec of the snapshot
+    app_version:      [4 + time.MIN_YYYY_DATE_LEN + 8]u8, // example: `dev-2026-09-23-a4084b3`
+    region_count:     u32,
+}
+
+Region_Header :: struct #packed #all_or_none {
+	name_size: u32,
+	data_size: u32,
+}
+```
+
+[ Snapshot_Header  ]
+[ Region_Header    ]
+[   name bytes     ]
+[   data bytes     ]
+[ Region_Header    ]
+[   name bytes     ]
+[   data bytes     ]
+[ etc..            ]
+
+## Diff Checking
+
+Use hashing per memory segment to do a sanity diff-check.
+
+```odin
+import "core:crypto/hash"
+
+data: []byte = ...
+
+digest := hash.hash_bytes(hash.Algorithm.SHA256, data)
+defer delete(digest)
+```