Improve formatting of braced lists.

Before:
vector<int> x { 1, 2, 3 };
After:
vector<int> x{ 1, 2, 3 };

Also add a style option to remove the spaces inside braced lists,
so that the above becomes:
std::vector<int> v{1, 2, 3};

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@182570 91177308-0d34-0410-b5e6-96231b3b80d8