Added initial sphinx documentation

This commit adds initial files for the Sphinx documentation system and
expanded checkcode.sh to include `doc8` as documentation checker. Also
added this checker to the dependencies for travis CI.

Signed-off-by: Claudius Heine <ch@denx.de>

scripts/checkcode.sh

@@ -8,4 +8,7 @@ pep8 $1/*.py $1/*/*.py || ERROR=$(expr $ERROR + 1)
 echo "Checking with pylint"
 pylint $1/*.py $1/*/*.py || ERROR=$(expr $ERROR + 2)
 
+echo "Checking with doc8"
+doc8  $1/docs --ignore-path $1/docs/_build || ERROR=$(expr $ERROR + 4)
+
 exit $ERROR