Discard icomplete-mode, use helm now
Fix cscope setup

使用 cscope 而不是 GNU Global，跟 ctags 有冲突的地方
Adopt git-gutter+
Setup auto-complete
auto-complete: add clang backend c++ and gtk+

Get include dirs:
- pkg-config --cflags-only-I gtk+-3.0
- g++ -v -x c++ -E
insert bracket by pair

use electric-pair-mode