[COMPILER] Initial compiler infra (#12)

nnvm/Makefile

nnvm/include/nnvm/compiler/contrib_op_param.h

nnvm/include/nnvm/compiler/op_attr_types.h

nnvm/include/nnvm/compiler/packed_func_ext.h

nnvm/include/nnvm/op_attr_types.h

nnvm/include/nnvm/top/README

nnvm/python/nnvm/_base.py

nnvm/python/nnvm/_ctypes/symbol.py

nnvm/python/nnvm/compiler/__init__.py

nnvm/python/nnvm/compiler/build_module.py

nnvm/python/nnvm/compiler/graph_attr.py

nnvm/python/nnvm/compiler/graph_pass.py

nnvm/python/nnvm/compiler/registry.py

nnvm/python/nnvm/graph.py

nnvm/python/nnvm/libinfo.py

nnvm/python/nnvm/runtime.py

nnvm/python/nnvm/symbol.py

nnvm/python/nnvm/top/__init__.py

nnvm/python/nnvm/top/attr_dict.py

nnvm/python/nnvm/top/nn.py