v0.8.1

General changes

• You can now assign coefficients to all column/row combinations using colwise
  in the experimental MILPModel backend.
• Non-existent indexes in sum_expr now produce a warning instead of an error. The missing indexes will be ignored (#202).

Bugfixes

• Fixed a bug were get_solution could return mixed up values when variables had partially similar names (eg: s[i] and bus[i]) by @hugolarzabal (#244).
• Fixed a bug on where an if-condition had an input with length != 1.
• Fixed some minor issues with newer data.table versions