clang-format: Set ContinuationIndentWidth: 3

This fixes the indentation of struct members, for
example, which were previously indented by 4 spaces.

Gbp-Dch: ignore

.clang-format

@@ -4,6 +4,7 @@ Language: Cpp
 TabWidth:          8
 UseTab:            Always
 IndentWidth:       3
+ContinuationIndentWidth: 3
 ColumnLimit:       0
 BreakBeforeBraces: Allman
 AccessModifierOffset: 0