Flattening an empty list with call_user_func_array does not work (warning), so we need to add a check...

V6.2.3: Fix custom functions defined in plugins (trigger returns an array of arrays, so we need to flatten it...)

V6.2.2: Add ZIPnumeric and ZIPalphanum variables; translate rule names after variable substitution, too

Translate rule names after variable substitution, too. This allows users to collect translatable rule names in a variable and then insert it into the final rule name

VMCoupon_V1.0: Add helper plugin to provide VM coupon discounts in the variables SalesPriceAfterCoupon and CouponValue

Fixes #32

Fixes #30
Fixes #31

Disable the CustomerNumber variable again (apparently it accesses a private property under some circumstances)

New variables:
- Shoppergroups
- groups
- UserID
- UserName
- isVendor
- isGuest
- CustomerNumber

Fixes issue #16

- Update setCartPrices from the latest VM version. This fixes multiple taxes.
  We now also call the original function, unless ShippingWithTax is used.
  This should be more robust than always using a copied/modified function.
- Ignore empty lines in the rules

V6.1.2: Fix issue with callbacks on PHP 5.3 (callbacks could only be strings when called as ->callback, so use call_user_func_array instead, which works on all PHP versions)

-) Scoping functions are not handled generally
-) Added evaluate_for_subcategories function
-) Added debug_cart and debug_products and debug_values variables

V5.99.1: Some more library refactoring, merging in changed from the WC shipping by rules plugin (getCosts returns array with further information, possibly multiple rates, etc.)

Signed-off-by: Reinhold Kainhofer <reinhold@kainhofer.com>