Add task for publishing to npm

[tschaub]

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).

[tschaub]

If anybody wants to test out the result, I've published an openlayers-test package. With Browserify (or other CommonJS loaders) you can get it by adding openlayers-test as a dependency in your package.json:

  "devDependencies": {
    "openlayers-test": "3.1.0-pre.4"
  }

And then in any module that depends on OpenLayers:

var ol = require('openlayers-test');

There is still an issue with the debug build in that it tries to load deps.js (which doesn't exist). I'll address that separately.

[tschaub]

d4763a0 makes it so deps.js is no longer requested in debug mode.

[elemoine]

Please merge. And +1 for the shell script.