v3.1.1

• Fixed UIntToOH(x, 1) invocation with x.width == 0 (#778)
• Suggest wrapping in Wire() or IO() in requireIsHardware (#827)
• Use Vec.apply instead of new Vec in VecInit.apply (#825)
• Remove extraneous traversal in cloneSupertype (#824)
• Fix UIntToOH for output widths larger than 2^(input width) (#823)
• Add test for zero-width Mems. (#821)
• Minor edits to wording in ErrorLog.checkpoint() for deprecations. (#817)
• Make Mem and SyncReadMem constructors private (#816)
• Add Module.currentModule for getting a reference to the current Module (#810)