clang-format: codify some of our conventions

1. We tend to use 2 spaces for indenting pre-processor directives,
when we do it. Unfortunately clang-format also counts header-guards
so not really recommended to use blindly on a header...

2. Add comments to namespaces, since the closing brace is simply
a brace with no further decoration.

3. Attach escaped new-lines on the left (instead of current: right).
Where 'right' will add the '\' characters on the far-right of our column
limit, 'left' will put them as far left as it can while having them
vertically aligned.

Change-Id: Ib5a836c76f7761d743e0100c83e7db609b959249
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Kai Koehne <kai.koehne@qt.io>

_clang-format

@@ -62,6 +62,8 @@ NamespaceIndentation: None
 
 # Allow indentation for preprocessing directives (if/ifdef/endif). https://reviews.llvm.org/rL312125
 IndentPPDirectives: AfterHash
+# We only indent with 2 spaces for preprocessor directives
+PPIndentWidth: 2
 
 # Horizontally align arguments after an open bracket.
 # The coding style does not specify the following, but this is what gives
@@ -85,6 +87,21 @@ ForEachMacros:   [ foreach, Q_FOREACH, BOOST_FOREACH, forever, Q_FOREVER, QBENCH
 # Break constructor initializers before the colon and after the commas.
 BreakConstructorInitializers: BeforeColon
 
+# Add "// namespace <namespace>" comments on closing brace for a namespace
+# Ignored for namespaces that qualify as a short namespace,
+# see 'ShortNamespaceLines'
+FixNamespaceComments: true
+
+# Definition of how short a short namespace is, default 1
+ShortNamespaceLines: 1
+
+# When escaping newlines in a macro attach the '\' as far left as possible, e.g.
+##define a     \
+#   something; \
+#   other;     \
+#   thelastlineislong;
+AlignEscapedNewlines: Left
+
 # Avoids the addition of a space between an identifier and the
 # initializer list in list-initialization.
 SpaceBeforeCpp11BracedList: false