this should make the integration code for hrixs more readable, and also fixes a bug.

See merge request !231

this removes more code from the inner loop. It is more efficient,
but is it also more readable? Probably not.

Manage exception in load_run_values()

See merge request !232

the curvature correction makes that the edges of our integration
range are not straight. We need to integrate over a larger range
then the resulting spectrum would suggest. Before this code we tried
that, but actually failed.

this documents the hRIXS class, and does some minor code cleanup.

See merge request !228

this documents the hRIXS class, and does some minor code cleanup.

fix bug with subset in get_array()

See merge request !230

These are the cumulative changes from said proposal. I left out the changes to load the tunnel XGM, as it was commented out later anyways, and probably should be done different anyways.

See merge request !224

that was a quick hack that should not be done, background subtraction is
the way to go.

Fix min distance in peak finding algorithm

See merge request !227

Undulator configuration

See merge request !225

Only use `select_trains()` when necessary

Closes #64

See merge request !226