Add package versions to OSGi metadata

[io7m]

This adds version declarations to each exported package in the
OSGi metadata. This allows users to specify that they want a
specific version (or range of versions) of JNA in their OSGi
applications/libraries.

Fix #975

[io7m]

I haven't touched the platform jar as there's something in there I'm not sure about: It uses Require-Bundle which is considered very bad practice in modern OSGi. I'd have to know if there was some specific reason this is being used before I go modifying the manifest.

[matthiasblaesing]

Thank you Mark, in general this would be ok to merge. Please also add an entry to CHANGES.md. Please see the other entries as a template.
In regard to the Require-Bundle problem - JNA and JNA platform are build together and released together so in this case you don't gain much by switching from bundle to package dependencies. For external users it might be worth adding the version to the exported packages of the platform, as the platform might be split in the future.

[io7m]

I've added the versions to the platform jar, and added an entry to CHANGES.md.

[io7m]

Not... sure what that build failure is about. I don't think it's related to the changes I made.

[matthiasblaesing]

Looks good - thank you for taking care of it.