Updates required for QAT

This MR includes:

• Abs operator;
• Hook system for Node (as suggested in #98 (closed) @thibaultallenet).
• Update of SinglePassGraphMatching to match no connection (with the special node keyword $).
• Solved some SinglePassGraphMatching issues and added more complex unit tests.
• Added missing inChannels() method for FC operator;
• Added matchFrom() method to SinglePassGraphMatching in order to match a query only for a specific starting node;
• Fix issue #87 (closed).

include/aidge/graph/Matching.hpp

@@ -160,7 +160,7 @@ private:
     bool matchNodeOrBlock(Context& ctx, std::set<MatchingResult>& matches);
 
     /**
-     * BLOCK = '(' SEQ | PAR | BLOCK | ALT | NODE ')'
+     * BLOCK = '(' SEQ | PAR | ALT | BLOCK | NODE ')'
     */
     bool matchBlock(Context& ctx, std::set<MatchingResult>& matches);
 
@@ -192,7 +192,7 @@ private:
      * TYPE = [A-Za-z0-9_]+
      * ANCHOR = [A-Za-z0-9_]+
      * LAMBDA = [A-Za-z0-9_]+
-     * NODE = (TYPE | '.') ('#' ANCHOR)? ('[' LAMBDA ']')?
+     * NODE = ((TYPE | '.') ('#' ANCHOR)? ('[' LAMBDA ']')?) | '$'
     */
     bool matchNode(Context& ctx, std::set<MatchingResult>& matches);