* Dev nas interface -- document (#1049)

* nas interface doc

* Dev nas compile -- code generator (#1067)

* finish code for parsing mutable_layers annotation and testcode

* Dev nas interface -- update figures (#1070)

 update figs

* update searchspace_generator (#1071)

* GeneralNasInterfaces.md: Fix a typo (#1079)
Signed-off-by: Ce Gao <gaoce@caicloud.io>

* add NAS example and fix bugs (#1083)

update searchspace_generator, add example, update NAS example

* fix bugs (#1108)

* Remove NAS example (#1116)

 remove example

* update (#1119)

* Dev nas interface2 (#1121)

update doc

* Fix comment for pr of nas (#1122)

 resolve comment