v0.8.7

Yao v0.8.7

Diff since v0.8.6

Closed issues:

• customed (random) unitary operation too hard to define (#449)

Merged pull requests:

• fix the error of applying diagonal gate to a GPU register. (#451) (@GiggleLiu)
• Added similar(::DensityMatrix) (#452) (@jlbosse)
• More work on basic error channels (#455) (@jlbosse)
• fix typo in 1.prepare-ghz-state/index.md (#457) (@eltociear)