pumpkin-checker-v0.4.0

Added

• (pumpkin-solver) Check derived nogoods during search (#373)
• (pumpkin-proof-processor) Introduce the proof processor in the main branch (#371)

Other

• Use central version number for all pumpkin-* crates (#470)
• (deps) bump assert_cmd from 2.2.1 to 2.2.2 (#445)