Mutability check on function arguments

[bvssvni]

Added a mutability check on function arguments. All function arguments are immutable by default.

• Mutability information is appended to function name, e.g. foo(mut a, b) is foo(mut,_)
• Pure functions have no mutability information, e.g. foo(a, b) is just foo
• Lifetime checker prevents assigning to immutable arguments
• Lifetime checker prevents calling a function taking a mutable parameter with an immutable argument
• Added function suggestions when declaration of a function can not be found
• Added function suggestions when expected different number of arguments to a function

Example:

fn foo(mut a, b) {
    a[0] = clone(b)
}

fn bar(a, b) {
    foo(mut a, b)
}

fn main() {
    a := [4]
    b := 5
    bar(a, b)
}

 --- ERROR --- 
In `source/test.rs`:
Requires `mut a`
7,13:     foo(mut a, b)
7,13:             ^

It is allowed to declare multiple functions with same name using different mutability patterns.

Example:

fn reset_x(pos) -> {
    return [0, clone(pos[1])]
}

fn reset_x(mut pos) {
    pos[0] = 0
}

fn main() {
    pos := [1, 2]
    println(pos)
    println(reset_x(pos))
    reset_x(mut pos)
    println(pos)
}