Adding a document that describes the architecture of data formatters. Suggestions and ideas for improvements most welcome

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@198038 91177308-0d34-0410-b5e6-96231b3b80d8
Fix sidebar links

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@198039 91177308-0d34-0410-b5e6-96231b3b80d8