feat: implement semver and changelog (#33)

[ynohat]

Added scripts/bump.sh to handle version increments, changelog generation and tagging.

I would like to merge this directly into master, since it cannot be tested on any other branch.

The release management process will be:

• development happens as usual on dev/feature branches
• once the PR is merged to master, the merger will pull the changes to their local repository and run one of

./scripts/bump.sh major # for breaking changes
./scripts/bump.sh minor # for backwards-compatible enhancements
./scripts/bump.sh patch # for fixes

Followed by:

git push --follow-tags # to push the updated changelog and the release tag

This will trigger a build for the tag.

The bump.sh script performs the following steps:

• increments the version
• generates the changelog from the commit history since the previous version
• allows the merger to edit the changelog (the intent is to allow cleaning up, adding an annotation to summarize the release etc...)
• assembles the complete changelog from the current version changelog and previous version changelogs into CHANGELOG.md
• commits the CHANGELOG.md file
• creates an annotated tag with the current version changelog as the tag annotation

[ynohat]

I should have marked this as a draft, there are a couple of details missing before this can be merged (mainly travis configuration to build tags). The review can start, however.