ENH: info class

This one addresses #645 

Looks like this, summarized and ordered by list:

```
<Info | 19 non-empty fields
    bads : list | 2 items
    buffer_size_sec : numpy.float64 | 13.3196808772
    ch_names : list | 306 items
    chs : list | 306 items
    comps : list | 0 items
    dev_head_t : dict | 3 items
    dig : list | 146 items
    file_id : dict | 4 items
    filename : unicode | 107 items
    filenames : list | 1 items
    highpass : float | 0.10000000149
    lowpass : float | 40.0
    meas_date : numpy.ndarray | 2 items
    meas_id : dict | 4 items
    nchan : int | 306
    orig_blocks : list | 5 items
    orig_fid_str : instance | <StringIO.StringIO instance at 0x114753f0>
    projs : list | 4 items
    sfreq : float | 150.153747559
    acq_pars : NoneType
    acq_stim : NoneType
    ctf_head_t : NoneType
    description : NoneType
    dev_ctf_t : NoneType
    experimenter : NoneType
    proj_id : NoneType
    proj_name : NoneType
>
```

If you like it I'll goo and replace our regular info dicts.