Add task for publishing to npm

This task publishes an existing tag to the npm registry.  To publish a new release, create a commit that updates the version number in package.json (e.g. to "3.1.0").  Then create a tag, push to GitHub, and run the publish task.  Assuming "openlayers" is the remote for the canonical repo, this would look like the following:

    git tag -a v3.1.0 -m "3.1.0"
    git push --tags openlayers
    ./tasks/publish.sh 3.1.0

The task creates a build for each of the `PROFILES` in `publish.sh` (these correspond to `.json` files in the `config` directory).  Builds are generated in the `dist` directory.  Our `package.json` specifies `dist/ol.js` as the "main" build.  So when people use a module loader to `require('openlayers')`, they get the full build.  It is also possible to load a debug build (e.g. `require('openlayers/dist/ol-debug')`), and we can publish additional builds by adding `config` files and updating `PROFILES` in `publish.sh`.

The `.npmignore` file determines what is *not* included in the package (note that `node_modules` are always ignored).  So if additional items are added to `.gitignore` that should not be included in the npm package, they need to go in `.npmignore` as well (ideally, we don't need to generate anything else outside of the `build` directory that doesn't belong in the package).

.gitignore

@@ -1,6 +1,7 @@
 *.pyc
-/build
+/build/
 /examples/*.html.png
 /examples/example-list.js
 /examples/example-list.xml
 /node_modules/
+/dist/

.npmignore

@@ -0,0 +1,5 @@
+*.pyc
+/build/
+/examples/*.html.png
+/examples/example-list.js
+/examples/example-list.xml

package.json

@@ -14,6 +14,7 @@
     "start": "node tasks/serve.js",
     "test": "node tasks/test.js"
   },
+  "main": "dist/ol.js",
   "repository": {
     "type": "git",
     "url": "git://github.com/openlayers/ol3.git"

tasks/publish.sh

@@ -0,0 +1,96 @@
+#!/bin/bash
+
+#
+# Run this script to publish a new version of the library to npm.  This requires
+# that you have a clean working directory and have created a tag that matches
+# the version number in package.json.
+#
+set -o errexit
+
+#
+# All profiles to be built.  Must correspond to .json files in the config
+# directory.
+#
+PROFILES="ol ol-debug"
+
+#
+# URL for canonical repo.
+#
+REMOTE=https://github.com/openlayers/ol3.git
+
+#
+# Display usage and exit.
+#
+display_usage() {
+  cat <<-EOF
+
+  Usage: ${1} <version>
+
+  To publish a new release, update the version number in package.json and
+  create a tag for the release.
+
+  The tag name must match the version number prefixed by a "v" (for example,
+  version 3.2.1 would be tagged v3.2.1).
+
+  The tag must be pushed to ${REMOTE} before the release can be published.
+
+EOF
+  exit 1
+}
+
+#
+# Exit if the current working tree is not clean.
+#
+assert_clean() {
+  source `git --exec-path`/git-sh-setup && \
+      require_clean_work_tree "publish" "Please commit or stash them."
+}
+
+#
+# Exit if the requested version doesn't match package.json.
+#
+assert_version_match() {
+  v=`grep -o '"version":.*' package.json | sed 's/"version": *"\(.*\)",/\1/'`
+  if test "${1}" != "${v}"; then
+    echo "Version mismatch: requested '${1}', but package.json specifies '${v}'"
+    exit 1
+  fi
+}
+
+#
+# Build all of the distribution profiles.
+#
+build_profiles() {
+  for p in ${@}; do
+    echo building dist/${p}.js
+    node ./tasks/build.js config/${p}.json dist/${p}.js
+  done
+}
+
+#
+# Check out the provided tag.  This ensures that the tag has been pushed to
+# the canonical remote.
+#
+checkout_tag() {
+  git fetch ${REMOTE} refs/tags/v${1}:refs/tags/v${1}
+  git checkout refs/tags/v${1}
+}
+
+#
+# Build all profiles and publish.
+main() {
+  root=$(cd -P -- "$(dirname -- "${0}")" && pwd -P)/..
+  cd ${root}
+  assert_clean
+  checkout_tag ${1}
+  assert_version_match ${1}
+  rm -rf dist
+  build_profiles ${PROFILES}
+  npm publish
+}
+
+if test ${#} -ne 1; then
+  display_usage ${0}
+else
+  main ${1}
+fi