inconsistencies in .sa output

[ltalirz]

Since I've anyhow written the parsers for the moment, I noticed some inconsistencies in the .sa format.

First an example output:

 @ HKUST-1.sa Unitcell_volume: 18280.8   Density: 0.879097   ASA_A^2:
        3545.59 ASA_m^2/cm^3: 1939.51 ASA_m^2/g: 2206.26 NASA_A^2: 0
        NASA_m^2/cm^3: 0 NASA_m^2/g: 0 Number_of_channels: 1
        Channel_surface_area_A^2: 3545.59 Number_of_pockets: 0
        Pocket_surface_area_A^2:

• Pocket_surface_area_A^2:
  is not followed by any number. This makes the format unnecessarily harder to parse.
  Better simply write 0.
• "Density": 0.748207 is lacking units
• "Unitcell_volume": 6415.16 is lacking units
• (minor) Strictly speaking, ASA_m^2/cm^3 and ASA_m^2/g should be renamed to ASA/V_m^2/cm^3, ASA/M_m^2/g , since they are not the same quantity as ASA (same for NASA)