1. Unix-like command api
2. 100% compatible with le.sh 1.x command api.
3. Support different webroot for each domain in the same cert.
```
le.sh --issue -d a.com -w /wwwroot/a.com -d b.com -w /wwwroot/b.com
```
4. Support different authentication methods for each domain in the same cert. Hybrid usage:
```
le.sh --issue -d a.com -w /wwwroot/a.com -d b.com -dns dns-cf
```
5. Two different debug levels to provide useful debug info. `--debug` or `--debug 2`
6. Support to install `fullchain.cer` after renewal.
7. Better performance.
