This commit adds support for parsing multiple parameters to both `ADD`
and `COPY` commands.
For example, tree-sitter-dockerfile now correctly parses both of these
lines from the dockerfile reference[^1]:
```dockerfile
ADD --chown=myuser:mygroup --chmod=655 files* /somedir/
COPY --chown=myuser:mygroup --chmod=644 files* /somedir/
```
Closes#43
[^1]: https://docs.docker.com/engine/reference/builder/
