renamed and slightly modified from get_log_ticks(), now with minor tick labels

to catch potential mismatches between the roxygen comments and the .Rd files. Closes #43

because some dependencies are not met in 3.5.0

3.5.0 beacause it is the earliest supported version as specified in DESCRIPTION. 3.6.3 because it is the last version before 4.0.0

Less output means it is easier to see the check results. If packages fail to install I can re-enable the output for the duration of the investigation.

closes #38

v2.7.0 - return stresses of predict_mixture()

See merge request !29

Improve ec() and axis concentration handling

Closes #35

See merge request !28

Replace the "use_for_plotting" column in mod$curves with the plot axis concentrations, which is far more useful.
Add "refence" argument to ec() and some minor improvements.

Some bugfixes and more flexible concentration lengths

See merge request !27

Control whether observed points are plotted

See merge request !26

* Add plotting control for the observed points and improve the generation of the legend. See the `which` argument in `?plot_ecxsys`.
* Renamed `sys_tox_not_fitted` and `sys_tox_env_not_fitted` to `sys_tox_observed` and `sys_tox_env_observed` in the output of `ecxsys()`.

Improve predict_mixture

See merge request !25