Release Version v0.2.1 Evolved!

We have been kept on developing HPC-NOW. This pre-release combines several efforts:

1. Introduced the interactive mode, now you can add -i to hpcopr to enter the interactive mode.
2. A more powerful HPC app store. Now you can specify and configure the backend locations. The locations can be http, ftp, or local directories.
3. Enhanced security: when adding a new cluster or setting password to a cluster user, the complexity of the password will be checked.
4. Fixed several known bugs.

Any fork, build, test, and issues are welcome.