Update and rename r.bilinear.txt to r.resamp.interp.txt

r.bilinear: merged into r.resamp.interp, see http://trac.osgeo.org/grass/wiki/Grass7/NewFeatures#Renamedmodules
Merge pull request #1693 from neteler/patch-5

Update and rename r.bilinear.txt to r.resamp.interp.txt