[lang][grammar] Support varargs parameters in action signatures

[srodriguez]

At the moments one can not declare varargs parameters in the signature of actions (used in capacity, agents,etc)
We should be able to declare
def myAction(String... params)
Instead of
def myAction(String[] params)

[gallandarakhneorg]

According to the current syntax, the varargs may be written as:

def myAction(params : String...)
def myAction(arg1 : boolean, arg2 : int...)

[srodriguez]

What do you think about using "*" instead of "...":

def myAction(params : String* )
def myAction(arg1 : boolean, arg2 : int* )

[gallandarakhneorg]

I prefer "...", but "*" seems to be a good option too.
I think that we should not support the twos for avoiding complexity in the language.

So, we are pat on this decision node. @ngaud should give his oppinion :-)

[ngaud]

Since Scala remains one of our main inspiration in terms of Syntax let's use the scala syntax with * to stay coherent.