Add command to export .stbl files

src/stbl/commands/__init__.py

@@ -1 +1,3 @@
-command_group = []
+from .export import export_command
+
+command_group = [export_command]

src/stbl/commands/export.py

@@ -0,0 +1,21 @@
+import json
+
+import click
+
+from stbl.stbl import STBLFile
+
+
+@click.command('export')
+@click.argument('stbl_file', type=click.Path(exists=True, dir_okay=False))
+def export_command(stbl_file):
+    """Export .stbl file in JSON format."""
+
+    stbl = STBLFile()
+    stbl.read(stbl_file)
+
+    if not stbl.validate():
+        raise RuntimeError(f'Invalid .stbl file format "{stbl_file}".')
+
+    data = list(map(lambda entry: {'instance': '0x' + ('%08x' % entry.instance_id).upper(), 'text': entry.text}, stbl.entries))
+
+    print(json.dumps(data, ensure_ascii=False, indent=4))