Try to describe our coding style using clang-format

How to use:

Install 'git-format-clang' which is part of the clang suite (Fedora:
git-clang-format, openSUSE: clang-tools).

Now do your changes and stage them with `git add`. Once they are staged
format the code using `git clang-format` before you commit.

Now the formatting changed can be viewed with `git diff` against the
staged changes.

Signed-off-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

.clang-format

@@ -0,0 +1,25 @@
+# https://clang.llvm.org/docs/ClangFormatStyleOptions.html
+BasedOnStyle: LLVM
+IndentWidth: 4
+UseTab: Never
+AllowShortIfStatementsOnASingleLine: false
+BreakBeforeBraces: Custom
+BraceWrapping:
+    AfterEnum: false
+    AfterFunction: true
+    AfterStruct: false
+    AfterUnion: false
+    AfterExternBlock: true
+    BeforeElse: false
+    BeforeWhile: false
+IndentCaseLabels: false
+ColumnLimit: 80
+AlignAfterOpenBracket: Align
+AllowAllParametersOfDeclarationOnNextLine: false
+BinPackArguments: false
+BinPackParameters: false
+AllowAllArgumentsOnNextLine: false
+AllowShortFunctionsOnASingleLine: Empty
+AlwaysBreakAfterReturnType: None
+AlignEscapedNewlines: Left
+ForEachMacros: ['ssh_callbacks_iterate']