Produce Maven packages for shared Javascript components

[io7m]

This change simply adds a Maven POM file that will produce a standard Java jar file that can be deployed to any Maven repository. This allows anyone using Maven (or a build system that uses Maven packages such as Gradle) to add the readium-shared-js components to their application without having to import any sources directly, or use git submodules.

The change is entirely opt-in: If you don't run Maven, you won't see anything new.

[danielweck]

Thanks @io7m
Would it make sense to also include build-output/_multiple-bundles/* in addition to build-output/_single-bundle/*? (just in case other developers need / want to use distinct RequireJS bundles, without the built-in lightweight Almond AMD loader)
Also, the version specified in pom.xml will have to be kept up to date with the JSON (well, CSON) NPM package definition:
https://github.com/readium/readium-shared-js/blob/develop/package.json#L8
https://github.com/readium/readium-shared-js/blob/develop/package.cson#L36
(we have a build task in readium-js-viewer that maintains the Chrome app version, so we could use something similar in readium-shared-js)

[io7m]

Yep, there's no technical reason for not adding multiple-bundles, I just sort of assumed that _single-bundle would be the one that everyone used. I think I would add a second pom.xml for those, so the user would pick which one they wanted at compile time.

[io7m]

Updating the version of the pom.xml file can be achieved with: $ mvn versions:set -DnewVersion=0.21.0.

[danielweck]

Re. version updating:
in readium-js-viewer, package.cson contains the "master" version that is used to generate / maintain the version in the Chrome app. See:
https://github.com/readium/readium-js-viewer/blob/develop/src/chrome-app/manifest.json#L5
https://github.com/readium/readium-js-viewer/blob/develop/build-config/updateChromeManifest.js

Perhaps mvn versions:set -DnewVersion=x.y.z could be automated in a similar fashion when generating the build-output/* contents of readium-shared-js (i.e. when invoking npm run build).

[rkwright]

Note: Need to review this with respect to updating the versions in the various deliverables

[rkwright]

ACTION: Mark is the owner. He will work with Daniel to ensure we are not introducing conflicts.

Note that there is a dependency on other PRs in SDK, SDK readium/readium-sdk#193

[io7m]

Ok, I've pushed the changes that were necessary. Currently, the version number is manually set to 0.20.0-alpha to match what's already in readium-shared-js. The POM itself had some metadata updates, as Central has some requirements for artifacts:

http://central.sonatype.org/pages/requirements.html

[io7m]

I suspect I'll be the one actually pushing the packages to Central, as I'm already set up to do so (have PGP keys, have a Sonatype account, etc).

[danielweck]

Note that no Readium NPM packages have been published yet to:
https://www.npmjs.com/~readium
(just placeholders at v0.0.0)

More specifically, the POM / Maven build artifacts (single RequireJS / AMD bundles) would eventually match the NPM ones (same "semantic versioning" strings):
https://www.npmjs.com/package/readium-shared-js
...although the NPM ones would include both single and multiple bundles, as per the files directive in package.json:
https://github.com/readium/readium-shared-js/blob/develop/package.cson#L72