Woohoo! `ckan install Whatever` now works!

Try this:

    ckan update
    ckan install kOS

Also includes a version class (closes #42).

This breaks the old install which can install from the cmdline.
We should fix that. :)
Allow the CKAN repo to be specified on the command line.

This is mostly useful for developers who wish to test their
CKAN-meta branches before merging upstream.

For example:

```
./ckan.exe update \
    --repo=https://github.com/pjf/CKAN-meta/archive/ModuleManager.zip
    --debug
```
Merge pull request #45 from pjf/set_repo

Install, update, available commands, plus custom repos.