Fix access to raw.X by .raw.{obs,var}_vector

Previously had relied on subsetting the entire object to get vector of X. Now just normalizes index.
Also stops throwing warning about changing behaviour. Whoops. scverse#171 (comment)

Export Raw (scverse#177)

Export raw from main namespace (scverse#174)

fixed setup.py

removed brief release description

Use unpack_index from our code (scverse#151)

release notes for 0.6.19

Fix categorical treatment with pandas 0.24

fixed to_df for sparse data

version 0.6.16

name test file test.empty.h5 to ignore it