* structure tutorials

* refine data element docs

* modify introduce

* fix comment

* fix comment

* fix comment

* refine docs of data element

* update

* resolve comments

* [WIP] abstract-data-structure

* update docs

* update

* update BaseDataSample

* fix comment and coverage 100%

* update and add _set_field

* update

* split  into base_data_element and base_data_sample

* update

* update

* update

* fix typo

* add unit tests of data abstract interface

* update

* update

* update docs of data element

* a draft of UT of datasample, to be finished

* update datasample test

* updata

* update

* fix comments

* fix comments

* fix comments

Co-authored-by: liukuikun <liukuikun@sensetime.com>

* update isort

* update

* update comments

* update

* update

* update

* fix bug in use cases

* resolve all comments

* add description of basedatasample

* rename meta_info to metainfo as meta is an adj.

* update

* resolve comments

* clean set data

* finished doc

* rephrase

* update

* resolve comments

* more clear organization

* rephrase

* rephrase

* replace 基础数据元素 by 数据元素

* rephrase