Add SumCost

'*' operator overload for LayerOutput

Making '*' support the multiplication between a scalar and LayerOutput

Also changing '+' to support adding between a vector and a scalar.

Change-Id: I7daf35590dc2b2f855a29d9ef43ac57979442e0f

Add bilinear interpolation layer

* set mixedlayer output size according to input operator
* change from num_channel to num_channels for conv_operator (the old one is
really misleading because all the others are num_channels)

* also changed the arg name in projections.py

Fix matrix inverse  unittest to be more robust

rebase deconv implementation with develop branch and resolve conflicts with pull#218 commit 45c81a41

* the memory leak is inside one pass.

Update cluster_train.md for easier understanding

* some tiny fixs

* use VLOG(3)

* make AVX_FOUND is default value to WITH AVX
* let AVX_FLAG always keep -mavx flag since compiler can build binary with -mavx even CPU does not support avx.