More bindings

[sogaiu]

This PR attempts to add a few more bindings (with tests) for:

• child_count
• named_child_count
• next_sibling
• prev_sibling
• next_named_sibling
• prev_named_sibling
• parent

There is also a binding for is_missing but it lacks a test as I don't have sample source for JavaScript or Python that produces that condition.

If someone has an example of that I might be able to add a test for it.

BTW, I ran the tests successfully with tree-sitter-python's tree-sitter-cli dev dependency in package.json set to something in the 0.16.x series as I failed to have the 0.17.x series (i.e. master branch) work with the tests.

See below for update.

[sogaiu]

So it looks like updating tree-sitter itself to tree-sitter/tree-sitter@5080de4 is sufficient to get the tests to pass.

I presume this is because of a change to TREE_SITTER_LANGUAGE_VERSION: https://github.com/tree-sitter/tree-sitter/blob/4c2f36a07b99732c96d474fdae30c1cf158b966e/lib/include/tree_sitter/api.h#L24

[maxbrunsfeld]

This all looks great. And you're right about the TREE_SITTER_LANGUAGE_VERSION bump. Thanks for doing the upgrade.