Number all code examples & add specification build to Makefile (#894)

* Merge makefile changes from dev/specification-fixes

- New top level makefile target: `specification`
  - Builds the specification document.

* Number all code examples.

This is more a change of convenience than anything. Referring to syntax
examples is much easier when they are numbered!

This commit is in the context of freechipsproject/firrtl#890 - Updating
examples and syntax specification is made easier if they are numbered.

- Change `verbatim` environments to `lstlisting`
- Add very basic keyword highlighting.
- Rebuild specification PDF.

 On branch dev/number-code-examples
 Changes to be committed:
	modified:   spec/spec.pdf
	modified:   spec/spec.tex

1 files changed, 5 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index c304f265..36e87949 100644
--- a/Makefile
+++ b/Makefile
@@ -9,9 +9,14 @@ scala_jar ?= $(install_dir)/firrtl.jar
 scala_src := $(shell find src -type f \( -name "*.scala" -o -path "*/resources/*" \))
 
 clean:
+	$(MAKE) -C $(root_dir)/spec clean
 	rm -f $(install_dir)/firrtl.jar
 	$(SBT) "clean"
 
+.PHONY : specification
+specification:
+	$(MAKE) -C $(root_dir)/spec all
+
 build:	build-scala
 
 regress: $(scala_jar)