Add registry and build_from_cfg (open-mmlab#195)

* add registry and build_from_cfg

* add some corner cases

* add some corner cases

* fix the unittest for python 3.5

* minor fix

remove support for python 3.4 (open-mmlab#189)

update version to 0.3.0 (open-mmlab#188)

fix the shape assertion in impad (open-mmlab#172)

Add dist utils (open-mmlab#157)

* add dist utils

* rename due to a typo

* bump version to 0.2.15

* fix imports

Add rgb2gray and gray2rgb (open-mmlab#139)

* add rgb2gray and gray2rgb

* update version

* minor fix for the docstring

Update version to v0.2.13 (open-mmlab#117)

update to v0.2.12 (open-mmlab#104)

update version to v0.2.11 (open-mmlab#98)

Fix the compiling bug when using `pip install mmcv` (open-mmlab#88)

* rename flowWarp to FlowWarp

* fix the compiling bug when using pip install

* update version to v0.2.10