Create silent template

This commit creates a template named `silent` which outputs nothing at
all.  As discussed in the `README.md`, this can be useful when running
JSDoc as a linter to check for syntax errors or unknown tags.  It may
also be useful for testing or benchmarking.

The same effect can be achieved using the haruki template and
redirecting the output to /dev/null, but this has a few downsides:

* It is non-obvious.
* It is difficult to do in scripts which must run in bash and cmd.exe
  (like npm scripts).
* It is slower due to the unnecessary formatting work and output
  syscalls.

This template could be distributed as a third-party template, but given
the tiny code size, broad applicability, and potential usefulness for
tests, it makes sense to include it officially.

Signed-off-by: Kevin Locke <kevin@kevinlocke.name>

templates/silent/README.md

@@ -0,0 +1,11 @@
+OVERVIEW
+========
+
+The `silent` template outputs nothing at all.  Why would that be useful?  Primarily for running JSDoc as a linter to check for syntax errors and unrecognized tags in documentation comments, although it may also be useful for testing or benchmarking purposes.
+
+USAGE
+=====
+
+    ./jsdoc myscript.js -t templates/silent -a all --pedantic
+
+This command exits with a non-zero exit code if any errors are encountered.  It writes nothing to disk and the only output it produces is any error messages written to `stderr`.  This command can also be used to warn about tags which are unknown to JSDoc by setting `"allowUnknownTags": false` in a configuration file.

templates/silent/publish.js

@@ -0,0 +1,8 @@
+'use strict';
+
+/**
+    @param {TAFFY} taffyData See <http://taffydb.com/>.
+    @param {object} opts
+    @param {Tutorial} tutorials
+ */
+exports.publish = function(taffyData, opts, tutorials) {};