Release 5.0.4

Release 5.0.2 on pub.dev

Release 5.0.1 on pub.dev

Release package to pub.dev as 5.0

update doc

1. fix cfug#877 'dio.interceptors.errorLock.lock()'

2. fix cfug#851
3. fix cfug#641

add test cases

Merge pull request cfug#639 from Endebert/patch-1

fix(transformer): reduce memory consumption

Merge pull request cfug#596 from HackrHIVE/patch-1

minor change in example (FormData)

revert cfug#562, and fixed cfug#566