Call to real SQL functions

[blixit]

In the 1st design, i forgot to include sql functions calls. It will be added to the 2nd version.
It should work like that :
SQL_CALL = 'identifier' '(' arg, ... ')'
arg = LValue or 'Identifier' or SQL_CALL

In a 'select' query, a field can be a SQL_CALL.
Ex : to get the average on the age field

: users {
AVG(age)
}

In a 'mutate_query', a right value can be a SQL_CALL.

: users {
token = SHA1('message')
}

These rules will be added to the syntax rules.