Some changes to Py_near_lines.
Some changes to Py_near_lines.

- Check the input type of the arrays.
- Declare a pointer of the right type outside the loop, avoiding all the
  expensive complicated numpy dereferences.
- Use a set not a vector to store the output. This means we get an
  ordered list of particles near lines, making the output the same
across calls, and hopefully making the later indexing faster.

sbird/fake_spectra,sbird/fake_spectra,sbird/fake_spectra