Add error code extension mechanism and use malformed currency code (#396)

Fixes #275

.githooks/pre-commit

@@ -6,7 +6,7 @@ exec 1>&2
 find src unittests -type f \( -name '*.cpp' -o -name '*.h' -o -name '*.ipp' \) -print0 | xargs -0 clang-format -i
 
 # check how many lines differ
-lines=$(git diff | wc -l)
+lines=$(git diff src unittests | wc -l)
 
 # check if there is any updated files
 if [ "$lines" != "0" ]; then