P3D-DFS v1.2 release

Main changes:

• Add support for the 0/1-Knapsack problem
• Extend support for PFSP (e.g., branching rule)
• Improve overall performance
• Update Chapel to 2.1.0
• Fix several bugs
• Clean code

P3D-DFS v1.1 release

Main changes:

• Add support for the N-Queens problem
• Update Chapel to 1.29.0
• Fix several bugs
• Clean code

P3D-DFS v1.0 release

Add initial support for solving instances of the Permutation Flowshop Scheduling Problem (PFSP) and Unbalanced Tree Search benchmark (UTS) using parallel depth-first tree search.