Add support for multi-line invocation

[nimmortal]

Hello,

I face an issue with contracts when I have function with many arguments.
For example, function has 8 arguments and I want to call it.
When I call with argument splitting for readability then the code will not be compiled.

OnBirth(owner, c_id,
            'a', 'b',
            'c', 'd',
            'e', 'f')

I need to change this to single line like that

OnBirth(owner, c_id,  'a', 'b', 'c', 'd', 'e', 'f')

The compilation error is
File "/usr/local/lib/python3.6/dist-packages/boa/code/expression.py", line 319, in lookup_method_name return self.methodnames.pop() IndexError: pop from empty list

Please, add such support otherwise it hit development experience.