Parameter changes and hiera usage

Hi,

I modified this puppet module a little bit.

I updated the params so that I can use it with Hiera, specifying the version I want to use on different machines.

What I did is:
- renamed param "avamar_host", now simply "host", default value is undef.
- renamed param "avamar_domain", now simply "domain", default value is 'clients'.
- added param "version", with a default value of '6.1.100-402'.

The only reason why I changed the params name is to make the Hiera config more readable:
```
avamar::host: 'avamar.domain.tld' # better than avamar::avamar_host: '...'
avamar::domain: 'clients'
avamar::version: '7.1.100-370'
```

I also added parameters to the avamar::params class, which is not very nice but it works.

I updated the read me to show how to use the module with and without Hiera

I tested it on Ubuntu 14.04 and had no problem installing the agent and registering the machine.

As this is changing the way to use the module, I suggest you add a 1.1.0 tag to the current state of the repo, before merging my changes.

Let me know if these changes are OK with you

Nicolas