dx_pttrn excludes COVID-19 codes

[mdbecker]

Thanks for the great package! We have a large DB of codes and DRGs assigned at a large regional hospital system and we've been looking at cases where this library disagrees with the billed DRGs. One high volume case is patients with a primary DX of U071 COVID-19. The CMS files show that these patients should be assigned DRG 177-179 but drgpy returns DRG 000. This seems to be due to dx_pttrn excluding these codes on line 6 of _mdcsrdr.py. I looked through the history and couldn't figure out why the code was written this way. Obviously this code was written before COVID-19. Is there a reason to exclude 'U' codes from this library? If not, may I submit a pull request to fix this?

Thanks!

[yubin-park]

@mdbecker sorry for this long overdue reply. I just pushed a fix on this. Thanks so much!