add cpp codestyle hooks

tools/codestyle/clang_format.hook

+#!/bin/bash
+set -e
+
+readonly VERSION="3.8"
+
+version=$(clang-format -version)
+
+if ! [[ $version == *"$VERSION"* ]]; then
+    echo "clang-format version check failed."
+    echo "a version contains '$VERSION' is needed, but get '$version'"
+    echo "you can install the right version, and make an soft-link to '\$PATH' env"
+    exit -1
+fi
+
+clang-format $@

tools/codestyle/cpplint_pre_commit.hook

+#!/bin/bash
+
+TOTAL_ERRORS=0
+if [[ ! $TRAVIS_BRANCH ]]; then
+  # install cpplint on local machine.
+  if [[ ! $(which cpplint) ]]; then
+    pip install cpplint
+  fi
+  # diff files on local machine. 
+  files=$(git diff --cached --name-status | awk '$1 != "D" {print $2}')
+else
+  # diff files between PR and latest commit on Travis CI. 
+  branch_ref=$(git rev-parse "$TRAVIS_BRANCH")
+  head_ref=$(git rev-parse HEAD)
+  files=$(git diff --name-status $branch_ref $head_ref | awk '$1 != "D" {print $2}')
+fi
+# The trick to remove deleted files: https://stackoverflow.com/a/2413151
+for file in $files; do
+    if [[ $file =~ ^(patches/.*) ]]; then
+        continue;
+    else
+        cpplint --filter=-readability/fn_size $file;
+        TOTAL_ERRORS=$(expr $TOTAL_ERRORS + $?);
+    fi
+done
+
+exit $TOTAL_ERRORS