The licence changes at this commit from GPL-3.0 to the GNU Affero General Public
License v3.0. Every commit from here onward is AGPL-3.0; everything up to and
including v9 is GPL-3.0. There is no gap between the two.

The difference that matters is section 13: a modified version run as a network
service must offer its users the corresponding source.

This release also corrects the provenance record. The simulator began from
The TYCHOSIUM (c 2018 Simon Shack, Patrik Holmqvist, GPL), which the README had
credited only as "inspiration"; ytliu0/ElpMpp02 (GPL-3.0) and REBOUND (GPL) are
attributed in the commits that follow. See NOTICE for what derives from each and
what does not, and data/PROVENANCE.md for third-party dataset rights.

GPL-3.0 and AGPL-3.0 combine under GPLv3 s13.