refactor store package

This update split stores to a sub package, code regeneration is required after update. Also some old import path won't work, need to fix fetcher.go and promise manually.

add metadata option to schema

v0.1.6

add metadata option to schema, update readme

generate command support custom path

v0.1.5

revert

bug fix and API improve

v0.1.3

fix store imports

add getM API and code refactor

Merge pull request #7 from Yiling-J/get_many

Add get many method

v0.1.1

Update README.md

first release

v0.1.0

Update README.md