Dials

We decided to use the release number 13 as [a reference marker for developers](https://github.com/dials/dials/issues/649issuecomment-468741232) to help migrating code changes to the upcoming DIALS 2.0 release.

* improved electron diffraction data support (ADSC-electron-57)

* EIGER/EIGER2 support updates for SPring8 (cctbx/cctbx_project282) and Diamond Light Source VMXi and I04 (cctbx/cctbx_project283)
* dials.image_viewer: Allow stacking of images (660)
* dials.image_viewer: Fix for mask tool

* dials.predict: switch index generation method for >50 images (585)
* xia2: bug fix for .h5 files where data files don't have 'data_' in file name (xia2/xia2272)
* Nexus file format support:
* add workaround if scan is None
* correctly interpret offset units

* EIGER detector support fixes
* dials.export_bitmaps: allow combining output_file with imageset_index
* xia2: fix character encoding in HTML log
* xia2: restore previously removed xia2.to_shelx command

* DIALS image viewer: show hdf5-derived file extensions in file load dialogue
* cosym: maintain experiment order as given in the input
* cosym: only export relevant experiments when using a subset of the data for analysis
* dials.reindex: sanity check space group before using a given reference
* dials.scale: speed up outlier rejection
* xia2: handle I2/C2 ambiguity in the dials-full pipeline (xia2/xia2260)
* xia2: general improvements to the dials-full pipeline