Implement Slasher

[gazayas]

code = <<~CODE
  10.times do |n|
    puts n
  end

  def n
    "n"
  end
CODE

msmn = Masamune::AbstractSyntaxTree.new(code)
msmn.replace(type: :variables, old_token: "n", new_token: "foo")

This will yield the following in string form:

10.times do |foo|
  puts foo
end

def n
  "n"
end