Replaces one string with another in a given string
    usage: {{ foo|replace:"aaa|xxx"}}

def replace(value, arg):
    """
    Replaces one string with another in a given string
    usage: {{ foo|replace:"aaa|xxx"}}
    """

    replacement = arg.split('|')
    try:
        return value.replace(replacement[0], replacement[1])
    except:
        return value