* remove block api

* remove clone_variable

* hide block inner apis

* update

* fix tests

* "add doc for exec"

* "add more changes"

* "fix based on preview"

* "chagne code format"

* "add doc for exec"

* "add more changes"

* "fix based on preview"

* "chagne code format"

* "init benchmark ops"

* "untrack outputs"

* "delete some usused code"

* "benchmark"

* "fix ci"

* "fix op test"

* "fix uint16 missing"

* "fix ci"

* "follow comments"

* "fix ci"

* "follow comments"

* "conficts. merge develop branch"

* repick

* "merge develop branch"

* "add float64 tests"

* "fix based comment"

* "fixed based comment"

* "polish code"

* "fix ci"

* "fix ci"

* "done"

optimize executor.run

When the second argument contains batch dimension, the axis should be 0.

Also makes elementwise ops more tolerant at handling tensors with trailing
singular dimensions.

fetch_var for getting the values of a variable with given name
get_var for getting the Variable with given name

* remove pick dependency

* fix bug

* small fix

* modify executor.py for save and load

* clean code

* Add usage example

* refine executor run function

* fix bug

* refine executor code

* fix block bug

* fix comments

* fix bug

* fix pass num