Improve macro hygiene

This commit improves hygiene and formatting of macro definitions
throughout the library. Specifically:
- It adds brackets around parameters to avoid unintended
  interpretation of arguments, e.g. due to operator precedence.
- It adds uses of the `do { ... } while( 0 )` idiom for macros that
  can be used as commands.

library/x509_crt.c

@@ -1444,7 +1444,7 @@ static int x509_info_subject_alt_name( char **buf, size_t *size,
     }
 
 #define CERT_TYPE(type,name)                    \
-    if( ns_cert_type & type )                   \
+    if( ns_cert_type & (type) )                 \
         PRINT_ITEM( name );
 
 static int x509_info_cert_type( char **buf, size_t *size,
@@ -1471,7 +1471,7 @@ static int x509_info_cert_type( char **buf, size_t *size,
 }
 
 #define KEY_USAGE(code,name)    \
-    if( key_usage & code )      \
+    if( key_usage & (code) )    \
         PRINT_ITEM( name );
 
 static int x509_info_key_usage( char **buf, size_t *size,