fix(): handle cases where brackets are not children of container

[AckslD]

closes #36

The issue with languages such as r is that the opening and closing brackets are not node-children of the container node. For example in r:

f(a, b)

has the tree:

(call) ; [1:1 - 7]
 function: (identifier) ; [1:1 - 1]
 "(" ; [1:2 - 2]
 arguments: (arguments) ; [1:3 - 6]
  (identifier) ; [1:3 - 3]
  "," ; [1:4 - 4]
  (identifier) ; [1:6 - 6]
 ")" ; [1:7 - 7]
"\n" ; [1:8 - 2:0]

whereas eg python (and all other languages I've seen) have something like:

def f(a, b):
    pass

with

(function_definition) ; [1:1 - 2:8]
 "def" ; [1:1 - 3]
 name: (identifier) ; [1:5 - 5]
 parameters: (parameters) ; [1:6 - 11]
  "(" ; [1:6 - 6]
  (identifier) ; [1:7 - 7]
  "," ; [1:8 - 8]
  (identifier) ; [1:10 - 10]
  ")" ; [1:11 - 11]
 ":" ; [1:12 - 12]
 body: (block) ; [2:5 - 8]
  (pass_statement) ; [2:5 - 8]
   "pass" ; [2:5 - 8]

ie the opening and closing brackets are part of parameters whereas in r it is part of function.