Added Clang Format File

Added .clang-format to specify the code format for the project.
It relies on the tool clang-format. clang-format is not shipped
in xcode command line tools. To use clang-format inside xcode
download and install clangformat-xcode
https://github.com/travisjeffery/ClangFormat-Xcode


This is as close as I could get from the options as I understand them, it matches closely to the style we specify only major difference i've noticed is a line break after assignment operator  if the statement takes it over the 100 column hard limit.
I'd probably make these two sections into bullets under Setting up Xcode.