Description

在全量迁移时 create table 阶段会执行 count操作，表创建完了，开始迁移数据时还会count。 所以create table阶段的 count操作可否省略掉。

Steps to reproduce the issue:
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Describe the results you received:

Describe the results you expected:

Output of ./dtle version:

(paste your output here)

**Additional information you deem important (e.g. issue happens only occasionally

npm WARN eslint-config-airbnb@16.1.0 requires a peer of eslint-plugin-jsx-a11y@^6.0.2 but none is installed. You must install peer dependencies yourself.
npm WARN eslint-config-airbnb@16.1.0 requires a peer of eslint-plugin-react@^7.4.0 but none is installed. You must install peer dependencies yourself.

![image](https://user-images.githubusercontent.com/10933561/71482033-c4544b80-2

Currently, the file that is passed has a hardcoded .txt and filename. We'd like to pass the filename in the headers of the QR codes.

Also, we'd like the files to work using Unicode.

Describe the bug
Documentation on form encoded serializer is incomple.

To Reproduce
Have someone who did not implement the feature try to understand what this feature does and how to use it only by reading the features documentation

Expected behavior
Have someone who did not implement the feature understand what this feature does and how to use it only by reading the features