update mobilenetv2 for seg

See merge request !51

update mobilenetv2 space

See merge request !50

# Conflicts:
#   paddleslim/nas/search_space/search_space_base.py

Fix backward searching in pruner.

See merge request !48

fix nas demo

See merge request !47

add distillation demo

See merge request !40

Fix init tokens of sa nas.

See merge request !46

Add tokens2arch function in sa nas class.

See merge request !45

update sanas demo

See merge request !39

Make block mask optional in sa nas.

See merge request !44

2. Fix unittest of sa nas

Move sensitive from analysis package to prune package.

See merge request !43

add single_distiller

See merge request !31

Fix sa nas

See merge request !38

Add save checkpoint function to sensitive pruner.

See merge request !41

Add sensitive pruner and demo

See merge request !37

add post training quantization api quant_post

See merge request !24