Added a make format command

Jens Wehnerrequested to merge
jenswehner/eigen:clang_format into master

Using make format formats the whole source code according to a .clang-format file, which specifies the exact layout.

This allows to later check if new Merge Request fulfill these guidelines.

The copyright on the FindCLANG_FORMAT can still be changed. : Done

Edited by Jens Wehner

Merge request reports