Released Chainer v6.4.0

[nis...@preferred.jp]

We have released Chainer v6.4.0. The release note is:

This is the release note of v6.4.0. See here for the complete list of solved issues and merged PRs.

Enhancements

• Insert missing spaces between concatenated string literals (#7935)
• Make parameterized test names deterministic (#8134)

Bug Fixes

• Fix decorrelated batch normalization when groups ≠ 1 (#7825)
• Support mixed16/float16 GroupNormalization (#8113)
• Fix deadlock on MultiprocessIterator and MultiprocessParallelUpdater (#8126)
• Fixes deepcopy for chain parameters (#8150)

Code Fixes

• Remove unused argument from decorrelated batch norm (#8097)

Documentation

• Add undocumented arguments to snapshot extension signature (#8016)
• Add a note about incompatibility with NumPy 1.17 + Python2 (#8028)
• Fix grammatical errors in documentation (#8036)
• Fix doc of backend.copyto (#8056)
• Fix typo (#8161)

Installation

• Fix NumPy version in Dockerfile (#8068)

Tests

• Refactor DecorrelatedBatchNormalizationTest and add stable input (#7940)
• Relax float16 tolerances in F.batch_inv test (#7981)
• Relax tolerances in old cuDNN convolution tests (#7982)
• Fix numerical gradient precision in F.squared_error test (#8012)
• Fix flaky negative_sampling (#8019)
• Relax tolerances in gradient_check test (#8021)
• Explicit h5py.File mode (#8107)
• Fix eps in Contrastive.backward (#8108)
• Remove duplicated parameter in test_normal.py (#8117)
• Fix macOS Travis error caused by Homebrew (#8118)
• Add timestamp to Travis CI log (#8119)
• Relax tolerance of im2col test (#8135)