Add documentation and source

Added documentation, source and extra files.

source/orm/library/models/loan.py

@@ -0,0 +1,29 @@
+from uuid import uuid4
+
+from django.db import models
+
+
+class Loan(models.Model):
+    """
+    Model for book loans.
+
+    """
+
+    uuid = models.UUIDField(default=uuid4, db_index=True, verbose_name="UUID")
+    person = models.ForeignKey("library.Person", on_delete=models.CASCADE, related_name="loans", verbose_name="person")
+    book = models.ForeignKey("library.Book", on_delete=models.CASCADE, related_name="loans", verbose_name="book")
+    date = models.DateTimeField(auto_now_add=True, verbose_name="date")
+    expected_return = models.DateTimeField(null=True, verbose_name="expected return date")
+    borrowed = models.BooleanField(null=True, default=True, verbose_name="borrowed")
+
+    class Meta:
+        verbose_name = "book loan"
+        verbose_name_plural = "book loans"
+        unique_together = [("book", "borrowed")]
+
+    def __str__(self):
+        return f"Book loan: {self.person} → {self.book}"
+
+    def return_book(self):
+        self.borrowed = None
+        self.save()