feat: implement packages structure and publication

[aeddi]

Description

The purpose of this PR is to make gomobile-ipfs available on Android/iOS package managers (Cocoapods and Gradle/Maven).

• Added a Manifest.yml file to centralize the configuration of the different packages
• Changed the Makefile rules and added utilities for formatting and publishing packages on Cocoapods/Maven
• Added javadoc in the Android bridge and markdown doc in the iOS bridge in order to:
  • Comply with maven's requirements
  • Provide documentation directly in the IDEs while using Bridge packages
  • Potentially, generate the documentation to put it online
• Added CI rules to lint, test and release packages:
  • Docs for Android and iOS is generated by CI and published on github-pages
  • A global changelog is generated by semantic-release/changelog
  • Version number and Github release are generated by semantic-release
• Cleaned up and reorganized folders

After discussion with my team, we chose to have a single version number for all packages (android/ios bridge/core/demo).
The version numbers of some packages will sometimes be bumped without changes, but it will be much easier to automate via the CI (tag, release, publish, etc...) and to use on the user side.

This PR requires to add secrets (Bintray, Cocoapods) in the repo settings to work.

As a second step, it would be nice to set up a Bintray repo in the name of IPFS, but I let the Protocol Labs teams take care of it so that they keep all sensitive information secret.

Related

• fixes [release] make pre-built lib available on Github releases and other platforms #12
• fixes feat: configure Semantic Releases #30
• fixes CI and release configuration #15
• closes build(deps): bump handlebars from 4.2.0 to 4.7.2 in /example/OBSOLETE_react-native #24
• closes Is there any policy/strategy for choosing a CI solution on the ipfs-shipyard organization? #29

[gfanton]

LGTM 👍