Remove debug logs (#27)

* Remove print (aka DEBUG log) in jflex() rule

* Make JFlex generation quiet by default.

* Make CUP generation quiet.

* Make the nested_grammar example non quiet.

It outputs
```
INFO: From jflex java/jflex/examples/nested_grammar/NestedRulesScanner.java:
Reading "java/jflex/examples/nested_grammar/nested_grammar.jflex"
Including "java/jflex/examples/nested_grammar/extra-jflex-rules.inc.jflex"
Constructing NFA : 18 states in NFA
Converting NFA to DFA :
............
14 states before minimization, 13 states in minimized DFA
Writing code to "bazel-out/darwin-fastbuild/bin/java/jflex/examples/nested_grammar/NestedRulesScanner.java"
```

cup/cup.bzl

@@ -20,12 +20,12 @@ def _cup_impl(ctx):
     args.extend(["-parser", ctx.attr.parser])
     args.extend(["-symbols", ctx.attr.symbols])
     args.extend(["-destdir", output_dir])
+    args.extend(["-nosummary"])
     if ctx.attr.interface:
         args.append("-interface")
     args.extend([ctx.file.src.path])
 
     # TODO(regisd): Add support for CUP options.
-    print("cup " + (" ".join(args)))
     parser_file = ctx.actions.declare_file(ctx.attr.parser + ".java")
     sym_file = ctx.actions.declare_file(ctx.attr.symbols + ".java")
     ctx.actions.run(

java/jflex/examples/nested_grammar/BUILD

@@ -6,6 +6,7 @@ jflex(
     srcs = ["nested_grammar.jflex"],
     data = ["extra-jflex-rules.inc.jflex"],
     outputs = ["NestedRulesScanner.java"],
+    quiet = False,
 )
 
 java_library(

jflex/jflex.bzl

@@ -21,9 +21,11 @@ def _jflex_impl(ctx):
     maybe_skel = [ctx.file.skeleton] if ctx.file.skeleton else []
     arg_maybe_skel = ["-skel", ctx.file.skeleton.path] if ctx.file.skeleton else []
     arg_maybe_jlex = ["--jlex"] if ctx.attr.jlex else []
+    arg_maybe_quiet = ["--quiet"] if ctx.attr.quiet else []
     arguments = (
         arg_maybe_skel +
         arg_maybe_jlex +
+        arg_maybe_quiet +
         # Option to specify output directory
         ["-d", output_dir] +
         # Input files
@@ -36,7 +38,6 @@ def _jflex_impl(ctx):
         executable = ctx.executable.jflex_bin,
         arguments = arguments,
     )
-    print("jflex " + (" ".join(arguments)))
 
 jflex = rule(
     implementation = _jflex_impl,
@@ -59,6 +60,10 @@ jflex = rule(
             doc = "an optional skeleton",
         ),
         "outputs": attr.output_list(allow_empty = False),
+        "quiet": attr.bool(
+            doc = "JFlex generation outputs error messages only",
+            default = True,
+        ),
         "jflex_bin": attr.label(
             default = Label("//jflex:jflex_bin"),
             executable = True,