command line wildcard file patterns aren't expanded on windows

[simonmichael]

Reported on chat: file wildcards (glob patterns) aren't expanded in a Windows CMD shell. This means that hledger import *.csv doesn't work on Windows (hledger sees a single *.csv argument instead of all the matched file paths). The bug is that docs should mention it (and workarounds such as powershell or bash), and the wish is to make hledger do the expansion when running on Windows (like the include directive does; PR welcome).