optimize code (zeromicro#579)

* optimize code

* optimize returns & unit test

fix golint issues (zeromicro#535)

fix type convert error (zeromicro#395)

simplify cgroup controller separation (zeromicro#384)

simplify cgroup controller separation (zeromicro#384)

simplify cgroup controller separation (zeromicro#384)

make sure offset less than size even it's checked inside (zeromicro#354)

optimize dockerfile generation (zeromicro#284)

require go 1.14 (zeromicro#263)

* refactor & format code

* optimized parse tag (zeromicro#256)

* feature plugin custom flag (zeromicro#251)

* support plugin custom flags

* add short name

* remove log

* remove log

* require go 1.14

Co-authored-by: kingxt <[email protected]>
Co-authored-by: songmeizi <[email protected]>

simplify code, format makefile (zeromicro#233)