Update coding guidelines

Add ranged-based for loop example
Add class inheritance example
Add Prefer pre-increment, pre-decrement operators section
Fix space after comment keyword
Fix header include order
[skip ci]

CODING_GUIDELINES.md

@@ -231,8 +231,8 @@ Example:
 
 #include <libtorrent/version.hpp>
 
-#include "base/bittorrent/session.h"
 #include "base/bittorrent/infohash.h"
+#include "base/bittorrent/session.h"
 #include "base/utils/fs.h"
 #include "base/utils/misc.h"
 #include "base/utils/string.h"
@@ -282,20 +282,32 @@ auto spinBox = static_cast<QSpinBox*>(sender());
 // we know the variable type based on the right-hand expression
 ```
 
-* Space around operations eg `a = b + c` or `a=b+c`:
+* Notice the spaces in the following specific situations:
-
-Before and after the assignment and other binary (and ternary) operators there should be a space.<br/>
-There should not be a space between increment/decrement and its operand.<br/>
-Some valid use cases:
 ```c++
+// Before and after the assignment and other binary (and ternary) operators there should be a space
+// There should not be a space between increment/decrement and its operand
 a += 20;
 a = (b <= MAX_B ? b : MAX_B);
 ++a;
-b--;
+--b;
 
 for (int a = 0; a < b; ++b) {
-    // code
 }
+
+// Range-based for loop, spaces before and after the colon
+for (auto i : container) {
+}
+
+// Derived class, spaces before and after the colon
+class Derived : public Base
+{
+};
+```
+
+* Prefer pre-increment, pre-decrement operators
+```c++
+++i, --j;  // Yes
+i++, j--;  // No
 ```
 
 * private/public/protected must not be indented