Release v2.1.0

This released version of remoll was used for the preparation of the March 2019 collaboration meeting. It includes a the following new features compared to v2.0 series (https://github.com/JeffersonLab/remoll/projects/9 for full view):

• correlated raster in the beam generator
• geometry reorganization

Known issues are:

• slow running due to some performance issues that are being addressed (#252)