copilot: Add hello world example for FPGA. Refs #657.

We need an example that demonstrates how to work with FPGAs using Copilot. This
will help users start with copilot-bluespec, and also help validate our work.

This commit adds a hello world example that demonstrates how to control 4 LEDs
from 4 switches. The tutorial describes how to install Vivado, create the spec,
compile it (in bluespec and then verilog), and upload it to the board.

Author: sukhmankkahlon

copilot/examples/fpga/HelloWorld/HelloWorld.hs

@@ -0,0 +1,19 @@
+module Main where
+
+import Language.Copilot
+import Copilot.Compile.Bluespec
+
+-- Define switches input
+sw :: Stream Word8
+sw = extern "sw" Nothing
+
+-- Define LEDS output
+leds :: Stream Word8
+leds = sw
+
+spec = do
+  trigger "leds" true [arg leds]
+
+main = do
+  spec' <- reify spec
+  compile "HelloWorld" spec'