Improved error handling

Wrote the traceback for any errors caught to item_nnn/stderr.out to aid debugging.

Cleaned up the printing.

Fixed missing printing and some small bugs introduced recently.

Catching errors inside loops

The version has two major enhancements:

1. Errors in the body of the loop are caught and can be ignored or handled in different ways at the direction of the user.
2. When looping over rows in a table, a query can be used to select the rows to operate on.

Updated for Python 3.8 and 3.9.

2021.10.13

Moving up to Python 3.8 and 3.9

Update for internal change in argument parsing.

2021.6.3

Updated for the seamm argument parser moving to seamm_util.

Added to the documentation.

Streamlined the documentation, adding a description for the plug-in.
Also tidied up the description for PyPI, which is used by the new installer, and added keywords to help with searches.

Updated for compatibility with the new system classes.

Merge pull request #16 from molssi-seamm/system2

Updated to be compatible with the new system classes.

Internal: moving to GitHub action for CI

No change in functionality, but making sure that everything works using GitHub Action for continuous integration (CI) and deployment (CD)

Moving to new command-line argument handling

Merge pull request #14 from molssi-seamm/option-handling

Updating for the new command-line argument handling

Minor bug fix for blocking bug with periodic systems.

2020.10.1

Fixed bug caused by incorrect indentation.