Use make as the main build tool

This allows us to start building real dependencies into Makefile.

Leave old hack/* scripts in place but advise to use 'make'.  There are a few
rules that call things like 'go run' or 'build/*' that I left as-is for now.

hooks/pre-commit

@@ -7,7 +7,7 @@ readonly green=$(tput bold; tput setaf 2)
 exit_code=0
 
 echo -ne "Checking that it builds... "
-if ! OUT=$("hack/build-go.sh" 2>&1); then
+if ! OUT=$(make 2>&1); then
   echo
   echo "${red}${OUT}"
   exit_code=1