Port over tests from npreadtext test suite
Port over tests from npreadtext test suite

- Add test for parsing scientific notation.
- Add multiple-char comment test.
- Port over tests for structured dtypes.
- Add tests for exceptions on skiprows/max_rows.
- port over ndmin tests.
- Make structured data reusable, add unpack tests.
- Port over delimiter tests.
- Port over maxrows test w/ various dtypes.
- Port over test of exception msg on parse failure.
- Port over test for converters w/neg indices.
- Port over usecols tests
- Port over unicode tests.
- Port over more converter tests.
- Port over test for large rows.
- Port over test for string-len discovery.
- Port over float conversion accuracy test.
- Port over bool test.
- Add test for implicit float->int conversion.
- Port over complex parsing tests.
- Port over tests for reading from generator.
- Port over object cleanup test.
- Port over bytes incompat test.
- Port over converters tests.

Co-authored-by: Warren Weckesser <2efebf2d11a67a14c829037bdd669d08c005fd4b@gmail.com>
Co-authored-by: Sebastian Berg <db043b2055cb3a47b2eb0b5aebf4e114a8c24a5a@sipsolutions.net>

endolith/numpy,numpy/numpy,anntzer/numpy,mhvk/numpy,charris/numpy,mattip/numpy,mhvk/numpy,rgommers/numpy,mhvk/numpy,jakirkham/numpy,mhvk/numpy,pdebuyl/numpy,seberg/numpy,seberg/numpy,jakirkham/numpy,numpy/numpy,pdebuyl/numpy,anntzer/numpy,mhvk/numpy,charris/numpy,mattip/numpy,rgommers/numpy,anntzer/numpy,charris/numpy,jakirkham/numpy,endolith/numpy,pdebuyl/numpy,rgommers/numpy,seberg/numpy,jakirkham/numpy,endolith/numpy,seberg/numpy,anntzer/numpy,charris/numpy,jakirkham/numpy,endolith/numpy,mattip/numpy,numpy/numpy,mattip/numpy,rgommers/numpy,numpy/numpy,pdebuyl/numpy