feat: Implement labels

[HendrikJanssen]

fixes #13

I did add the optional(label) to the statement sequence, also added expression statements since these were missing?

I am not really sure what happened with the for tests. From a glimpse, these were wrong before? A single increment_op was what I was expecting, not sure where the assignment came from beforehand, maybe someone can enlighten me what happened here?

I did not add labels to the break right now since I wanted to keep the changes minimal to be better to review. I will add these and quoted identifiers once I am more familiar with tree-sitter and have gathered feedback from this PR.

[murtaza64]

The way I designed the grammar I didn't want a plain _expression to count as a _statement. Not sure off the top of my head if this breaks anything... but if the tests aren't broken, I think it should be fine?

Adding _expression as a _statement explains why the for tests changed--an assignment node is inserted to promote i++ from an expression (increment_op) to a statement

[murtaza64]

Feel free to try implementing the rest of the label feature, as long as the tests stay passing and highlighting looks fine on typical code files I'm happy to merge it

[murtaza64]

If you fix the indentation I can merge this as-is

[HendrikJanssen]

Im going to come back to this PR on the weekend, I have much to do this week. But thank you very much for your time and explanation!

[murtaza64]

I managed to fix the indentation with the python script I wrote to help with the tests (python treesexpy/ts_test_helper.py corpus/label.test which diffs the output from treesitter with the test and shows you a line by line diff, optionally updating the test)

[murtaza64]

Thanks for the PR!