Support subdirectories in format string paths (#182)

* Create parent directories for format string paths

* Document format string fields and subdirectory support in CLI help

* Add format string options documentation

Author: bendwyer

README.md

@@ -165,8 +165,25 @@ kobodl book get \
   --output-dir /path/to/download_directory \
   --format-str '{Title}' \
   --get-all
+
+# Download books organized into subdirectories by author
+kobodl book get \
+  --output-dir /path/to/library \
+  --format-str '{Author}/{Title}' \
+  --get-all
 ```
 
+### Format string options
+
+The `--format-str` option supports the following fields:
+- `{Author}` - Book author(s)
+- `{Title}` - Book title
+- `{ShortRevisionId}` - First 8 characters of the revision ID (useful for avoiding filename collisions)
+
+You can use `/` in the format string to organize books into subdirectories. For example:
+- `'{Author}/{Title}'` creates `Author Name/Book Title.epub`
+- `'{Author} - {Title} {ShortRevisionId}'` creates `Author Name - Book Title a1b2c3d4.epub` (default)
+
 Running the web UI
 
 ``` bash

kobodl/actions.py

@@ -266,6 +266,7 @@ def GetBookOrBooks(
 
         try:
             click.echo(f'Downloading {currentProductId} to {outputFilePath}', err=True)
+            os.makedirs(os.path.dirname(outputFilePath), exist_ok=True)
             kobo.Download(bookMetadata, book_type == BookType.AUDIOBOOK, outputFilePath)
         except Exception as e:
             if productId:

kobodl/commands/book.py

@@ -43,7 +43,12 @@ def book():
     '--format-str',
     type=click.STRING,
     default=r'{Author} - {Title} {ShortRevisionId}',
-    help=r"default: '{Author} - {Title} {ShortRevisionId}'",
+    help=(
+        "Format string for output filename. "
+        "Available fields: {Author}, {Title}, {ShortRevisionId}. "
+        "Use '/' to create subdirectories (e.g., '{Author}/{Title}'). "
+        "Default: '{Author} - {Title} {ShortRevisionId}'"
+    ),
 )
 @click.argument('product-id', nargs=-1, type=click.STRING)
 @click.pass_obj