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/scrambler/scrambler.v

@@ -0,0 +1,14 @@
+module scrambler(
+        input clk, rst, in_bit,
+        output reg out_bit
+);
+    reg [31:0] xs;
+    always @(posedge clk) begin
+    	if (rst)
+	    xs = 1;
+        xs = xs ^ (xs << 13);
+        xs = xs ^ (xs >> 17);
+        xs = xs ^ (xs << 5);
+        out_bit <= in_bit ^ xs[0];
+    end
+endmodule