Adds human readable format for memory.

* CLI: The display of memory in `cci details` and `cci list` with the 'table'
       format (default) will display humanized RAM sizes '1G', '2G', '3G'.
* CLI: Re-implements the interface we use from Pretty-table and makes a method
       that can return a PrettyTable from a Table instance. This decouples the
       library code from our use of it. The new way support alignment, sorting,
       formatting columns and formatting specific row entries.
Merge pull request #33 from sudorandom/issue_27

Adds human readable format for memory.