doc: Replace grass.script by grass.tools

[wenzeslaus]

Replaces grass.script run_command calls by grass.tools in the main documentation. This will eventually include wording about the stability of the API.

old	new

[echoix]

I have a general question here. Do we have an idea of the performance difference between both usages? Maybe hard to evaluate, but it will be one of the most used code paths at one point

[wenzeslaus]

Performance: Just from the code analysis, there will be only a small difference at this point. Something goes to the attribute lookup and then to the StringIO identification. There will be more if we add, and by default enable, some of the other features, especially the pack IO adds extra cost.

Anyway, at this point, there is no significant difference:

$ grass ~/grassdata/nc_spm_08_grass7/PERMANENT/ --exec python -m timeit -n 100 -c "import grass.script as gs; gs.read_command('g.region', flags='p')"
100 loops, best of 5: 32.1 msec per loop
$ grass ~/grassdata/nc_spm_08_grass7/PERMANENT/ --exec python -m timeit -n 100 -c "from grass.tools import Tools; tools = Tools(); tools.g_region(flags='p').text"
100 loops, best of 5: 32 msec per loop

[echoix]

I used a spell check software after noticing a couple odd places.

[echoix]

Letting you finalize the commit message