Pyspextools

- Fixed ogipgenrsp which now uses the rmf structure with multiple MATRIX extensions.
- Added a force_poisson option to PHA reading routine and ogip2spex for cases where other
types of statistics are used and Poisson is desired.
- Added code to fix bins with zero width in ROSAT response matrices.
- Added tutorial about how to create .spo and .res files with more complicated sectors and regions.

- Discontinued Python 2 support.
- SPEX spectra and responses are now written in double precision.
- Fix for converting spectra from LEM and HEX-P responses where channel numbers are shifted by 1.
- Fix for converting spectra from rgscombine.

- Added capability to read and convert OGIP RMF files with multiple MATRIX extensions.
- Updated apec.py to work with pyatomdb 0.8.0 and above.

- Fixed issue with reading multiple res and spo files.
- Consistently changed pyspex to pyspextools in anticipation of the pyspex release with SPEX 3.06.00.
(Thanks to Anna Ogorzałek for reporting these issues).

- Not released.

- Updated apec.py example script for pyATOMDB >= 0.6.0 (only supports Python 3 now).
(Thanks to Francois Mernier for reporting.)
- Added no-area option to the ogipgenrsp script.