UNIT in &CELL and UNIT for output

[Teodoro Laino]

Dear All,

A major rearrangement of the UNIT keyword in the CELL section was required.
The reason is that, the UNIT keyword was to be considered an old 
duplicate compared to the more
advanced way we can treat units (i.e. specifying them within square 
brackets []), and this was posing
severe issues, more technical (code specific) than user perspective.
 
Therefore this is how the code has been updated:
1) UNIT keyword has been deleted from CELL section
2) keyword A,B,C and ABC have now units (to specify a cell in bohr 
therefore is enough to
    input something like ABC [bohr] x y z)
3) the units for the coord section can be specified now with two 
specific keywords in &COORD section
    COORD%UNIT  (by default angstrom)
    COORD%SCALED (by default set to FALSE)
    The first one accept a string (all units defined in CP2K can be 
input). The second one is a boolean.
    The units for the cell and for the coordinates have been now fully 
disentangled (you can use all kind
     of combinations you like)

The sad part:
This change will break unavoidably all old input files, but the 
modifications to be done to make them compatible
with the new version are minor (just follow the few steps above).

The innovation:
Moreover, since quite few people ask from time to time about units of 
output quantities, the last commit introduces, as well, the possibility 
to specify a unit of measure for quantities in output.
As you can imagine this would require a huge amount of work and the plan 
is to do it slowly.
Therefore at the moment very few print_key support the UNIT keyword. 
Possible requests to extend it
to other print_keys are well accepted and encouraged. All 
requests/comments can be posted on this thread.

Luckily this should be one of the last dinosaurs in CP2K (i.e. there 
should not be other major changes
that break so deeply the compatibility between CVS shapshots).
My apologies for this inconvenience.
Teo