* lbfgs right version

* delete log

* code_style

* add test

* delete sparse grad

* add test for converage

* modify example in dygraph

* revert lbfgs

* add test for linesearch

* code_style

* add test

* modify test

* modify test

* modify set

* modify set

* modify test

* modiy code_block; test=docs_preview

* modiy code_block; test=docs_preview