docs: moving code examples

Code now resides in `docs/source/code_examples`.
`CHAPTER_Prog` -> `stubnets`
`APPNOTE_011_Design_Investigation` -> `selections` and `show`
`resources/PRESENTATION_Intro` -> `intro`
`resources/PRESENTATION_ExSyn` -> `synth_flow`
`resources/PRESENTATION_ExAdv` -> `techmap`,  `macc`, and `selections`
`resources/PRESENTATION_ExOth` -> `scrambler` and `axis`

Note that generated images are not yet configured to build from the new code locations.

docs/source/code_examples/synth_flow/techmap_01_map.v

@@ -0,0 +1,24 @@
+module \$add (A, B, Y);
+
+parameter A_SIGNED = 0;
+parameter B_SIGNED = 0;
+parameter A_WIDTH = 1;
+parameter B_WIDTH = 1;
+parameter Y_WIDTH = 1;
+
+input [A_WIDTH-1:0] A;
+input [B_WIDTH-1:0] B;
+output [Y_WIDTH-1:0] Y;
+
+generate
+  if ((A_WIDTH == 32) && (B_WIDTH == 32))
+    begin
+      wire [16:0] S1 = A[15:0] + B[15:0];
+      wire [15:0] S2 = A[31:16] + B[31:16] + S1[16];
+      assign Y = {S2[15:0], S1[15:0]};
+    end
+  else
+    wire _TECHMAP_FAIL_ = 1;
+endgenerate
+
+endmodule