docstrings support added

[ThakeeNathees]

def foo()
  "
  pocketlang now supports, docstrings. This is similler to python's (because it's easier to parse)
  If a string literal is found before any statements inside a function it'll consumed as docstring.
  And thay will be added to the function with name `_docs` (foo._docs) will return this string.
  "
end

print(foo._docs)