add sync function for incremental update (#84)

* fishjam#1

add go.mod and fix build error(infini.sh/framework, fasthttp, util)

* run following command to format code:
  gofmt -l -w .

* fishjam#1

1.add Config: SortField, TruncateOutFile, SkipFields, so can dump es index to local file and compare.
2.add Config function: Sync , so can scroll and compare the source and dest index records, and just index/update/delete the changed records
3.refactor code:
  - add some functions in esapi, ClusterVersion() and DeleteScroll(), add ParseEsApi
  - move bulk.go to migrator.go, and add some functions
  - refactor all http method(GET/Post/DoRequest) to sinle Request method, and support proxy.
  - delete some commented and useless code

* fix error while source index not exist and change log.

* change model name

* change log

* update README.md and change the description of some configurations

add tips

Merge branch 'master' of github.com:medcl/esm-v1

Update README.md

Add FAQ

Update README.md

Add FAQ

fix number decode, Closes #36

fix routing breaking change between versions

update http to support new version

enable to skip cluster status check, use index instead of create for …

…bulk operations

update example