* REDIS-URL -> META-URL

* META-ADDR -> META-URL

* dump metadata into STDOUT

* update docs

* docs: add dump/load commands

* docs: address comments

* docs: translate command_reference to Chinese

* docs: remove experimental tag of `profile` command

* docs: minor fix

* address comments

* cmd: add `backup` command to dump Redis meta to a file

* cmd/backup: add support for SQL meta

* cmd/backup: add -i/--import to load metadata from a file

* cmd/backup: (Redis) re-calculate counters when importing metadata

* cmd/backup: (SQL) re-calculate counters when importing metadata

* cmd/backup: handle delfiles and sustained

* cmd/backup: ignore root inode when calculating usage

* cmd/backup: fix counters

* cmd/backup: calculate slice refs when loading

* cmd: split `backup` to two seperate commands: `dump` & `load`

* address comments

* test: add unit test for meta load/dump

* prepare for windows

* build for windows

* build for windows

* git diff

* remove libfuse-dev

* cleanup

* build juicefs.exe in Linux

* make with sudo

* fix travis

* fix travis

* add license header

* size of dir

* no syslog and run-in-background in windows

* fix compatibility with windows 10

* graceful umount

* fix build in Windows

* Add path based API

* fix build

* fix lint

* fix lint

* cleanup

* fix log format

* fix log format

* fix lint

* cleanup