two code walkthroughs: simplifying ASTs before icode, and seeing invocations for implicits at the AST level

Hi,

I've polished these days some draft notes that were on my to-do list
(attached). Pointers to similar documentation efforts are welcome.

As usual, the notes are also made available under
http://www.sts.tu-harburg.de/people/mi.garcia/ScalaCompilerCorner

Miguel