doc com.txt: use "Groonga" notation
doc cooperation.txt: use "Groonga" notation
doc document.txt: use "Groonga" notation
doc query.txt: use "Groonga" notation
doc test.txt: use "Groonga" notation
doc release.txt: use "Groonga" notation
doc contribution.po: use "Groonga" notation
doc: remove trailing spaces
Merge pull request #136 from cosmo0920/use-Groonga-notation-contribution

doc: use "Groonga" notation contribution/*.txt

Patch by cosmo. Thanks!!!