v0.8.0

General changes

• Removed dplyr dependency
• Added MILPModel, a new, vectorized backend for mixed integer linear programs that can handle very large models. It will eventually replace MIPModel.
• Added two functions (get_column_duals, get_row_duals) to extract the dual (column and row) values from an LP.
• The minimum supported R version is now 3.2.0
• get_solution now always return a solution, even if the solution status is not optimal.
• get_solution has a third argument type with permitted values being "primal" and "dual" to return the respective column primal or dual values.

Bugfixes

• You can now extract solutions of indexed variables that have length one (#198)