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/memory_01.v

@@ -0,0 +1,9 @@
+module test(input      CLK, ADDR,
+            input      [7:0] DIN,
+	    output reg [7:0] DOUT);
+    reg [7:0] mem [0:1];
+    always @(posedge CLK) begin
+        mem[ADDR] <= DIN;
+	DOUT <= mem[ADDR];
+    end
+endmodule