Newportxps

many bug fixes and features, but may need additional testing before tagging and releasing 1.0.0

- update to using pyproject.toml, install with `pip install newportxps`
- drop support for Python 2. Python 3.8 or higher is supported.
- remove getting host-by-name at initialization.
- add MultipleAxesPTExection and Verification (PR 16, Tom O'Brien)
- add support for HXP-D hexapod controller (PR 14, lockhart)
- better cleaning of text data before uploading to the controller.
- corrections to upload_stagesini (PR 12, LincolnUerhara)
- add command to clean TMP and CoreDump folders for controllers that support this (PR 13 skordaschristofanis)
- add functionality to set and get AquadB prescalers (PR 11, voloved)
- add features to list, upload, download, execute, and delete TCL scripts (PR 10, LinconlUehara)
- fix passing password credentials for FTP (PR 8, Nico-Helmi)
- fixes to byte encoding for ftp.
- `run_trajectory` will run `arm_trajectory` only if needed.
- tweaks to the waiting for a valid number of gathering points, better handling of errors when reading gathering file.

add pystfp as a requirement in setup.py
add a better error message about failed pyftp connections, with a hint about authorized keys
use posixpath for joining paths of files on ftp server