Implement a partial billing command

vultron/cmds/__init__.py

@@ -1,4 +1,13 @@
-# FIXME: build this dynamically
-__all__ = [
-  "account", "application", "backup", "help", "region", "vpc"
-]
+import os
+import pathlib
+
+# Not pretty but it works
+
+CMD_PATH = os.path.dirname(pathlib.Path(__file__).absolute())
+__all__ = [ ]
+
+for file in os.listdir(CMD_PATH):
+  path = os.path.join(CMD_PATH, file)
+
+  if os.path.isfile(path) and file.endswith(".py") and file != "__init__.py":
+    __all__.append(file[:-3])

vultron/cmds/billing.py

@@ -0,0 +1,15 @@
+import vultron.cmd
+
+class Billing(vultron.cmd.Command):
+  def vultron_list(self): # == billing history list (lists all payments and voices)
+    """Display all billing history."""
+
+    billing = self.api.get("billing", "history")
+    return billing["billing_history"]
+
+  def vultron_invoices(self): # == billing invoice list
+    invoices = self.api.get("billing", "invoices")
+    return invoices["billing_invoices"]
+
+# billing invoice get <id> is a specific entry from vultron_invoices
+# billing invoice items <id> gets all entries of the invoice