Bump version to 0.17.6

modified: Cargo.toml

Bump version to 0.17.5

Dev 0.17.4 (#282)

* Rename feature 'no_clause_elimination' to 'clause_elimination'
* Move ClauseIF to clause.rs; ClauseDB and ClauseDBIF to db.rs
* Move Var to var.rs and AssignStack to stack.rs
* Pull back ClauseDBIF to cdb/mod.rs
* Move AssignStack::assign to Var
* Move AssignStack::level to Var
* Move AssignStack::reason to Var
* Move AssignStack::reason_saved to Var
* Fix bug: dead clauses were not recycled
* Bump version to 0.17.4
* Update toolchain

Version 0.17.3

bump version to 0.17.2

bump version to 0.17.1