Remove r.statistics module and prepare documentation for its removal

[wenzeslaus]

Glynn C ([GRASS-dev] r.statistics in G7, March 28, 2014):

Martin L:

after discussion in OSGeo Vienna Code Sprint - r.statistics2 has been renamed in trunk to r.stats.zonal and r.statistics3 to r.stats.quantile

In which case, r.statistics should probably be removed altogether.

It has been (almost completely) superseded by the other two modules (a fact which is less likely to be noticed in light of the renaming).

The only functionality which isn't available via the other modules is the mode calculation. The main reason being that the new modules assume floating-point data (r.statistics uses r.stats which is based upon categories), for which the concept of "mode" isn't particularly meaningful.

It seems to me that the mode calculation is now available in r.mode, so there is no reason to keep r.statistics. Since it is removal of a module, we might not be able in version 7 unless somebody has some idea how to do it without breaking the interface.

In the meantime, we should remove links to r.statistics from other modules, improve their documentation (r.statistics has better docs then the other modules), and put some info to r.statistics that is is depreciated (we probably don't have a clear way how to do that). This might be nice to have even for 7.0.4, so if somebody volunteers to do that, it would be great, I won't get to this in the following weeks.

Finally, we should be checking if r.statistics can be really removed. If somebody is using it, please speak up.