Add a complete description of macros

Author: nicolasstucki

docs/docs/reference/dropped-features/macros.md

@@ -3,9 +3,10 @@ layout: doc-page
 title: Dropped: Scala 2 Macros
 ---
 
-The previous, experimental macro system has been dropped. Instead,
-there is a cleaner, more restricted system based on two complementary
-concepts: `inline` and `'{ ... }`/`${ ... }` code generation.
+The previous, experimental macro system has been dropped. Instead, there is a cleaner, more restricted system based on two complementary concepts: `inline` and `'{ ... }`/`${ ... }` code generation. 
+`'{ ... }` delays the compilation of the code and produces an object containing the code, dually `${ ... }` evaluates an expression which produces code and inserts it in the surrounding `${ ... }`.
+In this setting, a definition marked as inlined containing a `${ ... }` is a macro, the code inside the `${ ... }` is executed at compile-time and produces code in the form of `'{ ... }`.
+Additionally, the contents of code can be inspected and created with a more complex reflection API (TASTy Reflect) as an extension of `'{ ... }`/`${ ... }` framework.
 
 * `inline` has been [implemented](../other-new-features/inline.md) in Dotty.
 * Quotes `'{ ... }` and splices `${ ... }` has been [implemented](../other-new-features/principled-meta-programming.md) in Dotty.