Merge pull request chainer#1885 from pfnet/ver1.18.0

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Merge pull request chainer#1782 from pfnet/v1.17.0

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Merge pull request chainer#1688 from pfnet/v1.16

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Merge pull request chainer#1619 from pfnet/v1.15.0.1

update version to v1.15.0.1

Merge pull request chainer#1607 from pfnet/v1.15.0

update version to v1.15.0

Merge pull request chainer#1545 from pfnet/v1.14.0

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Merge pull request chainer#1476 from pfnet/v1.13.0

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Merge pull request chainer#1428 from pfnet/v1.12.0

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Merge pull request chainer#1377 from pfnet/v1.11.0

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Merge pull request chainer#1326 from pfnet/v1.10.0

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