Maintain signed version tags for release and manage deployment checkouts

Do cryptographically-verified checkouts of signed tags, or add new signed tags, with version numbers based on the current checkout. Three ordinals are used to represent version info, ala the Semantic Versioning scheme.

• releases (new tags) are prefixed with the branch name on which the tag occurred, and the new version number, relative to the last one
• deploys (checkouts) select the target tag after first narrowing matches to prefix of the current checkout (as determined by git describe) and doing requested math if relative (i.e. 'next', 'prev')

Subcommands are provided for tagging, checkout, and initialization: git reltag <subcommand>

• deploys can checkout a specific tag, the one before or after the checked out one, or the last one that tagged the deploy's parent branch.
• releases add a new signed tag, incrementing any of the three ordinals (resetting less significant ones to zero); a subcommand is provided for each of these intentions.

On a new clone of master, to set up to follow the lastest tag:

git checkout @ && git reltag

After the first time, only the latter command is needed to update to the lastest signed tag. The script presumes to run in deploy mode if the current branch tip is detached, it will pull and checkout latest tag in current branch. Otherwise it will do a release, defaulting to patch-level tag bump, and push.

If no subcommand specified, default depends on current checkout:

• refuses action in uncommitted repos (dirty work area) unless --dirty
• for tagging ops, checkout must have had commits since last tag
• warns if checking out on branch (usual case is sync from detached tag)

1. initialize repository we'll use for development:

   $ git init develop
   Initialized empty Git repository in /tmp/project/develop/.git/
   

2. add our first file to the project:

   $ cd develop
   $ touch testfile
   $ git add testfile
   $ git commit -m 'first checkin'
   [master (root-commit) 37e4ff1] first checkin
    1 file changed, 0 insertions(+), 0 deletions(-)
    create mode 100644 testfile
   

3. clone the development repo into the deploy location:

   $ cd ..
   $ git clone -q develop deploy
   

4. do our first release (using 'init' since no prior tags):

   $ cd -
   /tmp/project/develop
   
   $ git reltag init
   tag master-0.0.0 successfully created, commit message:
   branch: master
   commit: 37e4ff1c5e78662d2c67d4f88265dd5e00417ebd
   tagname: master-0.0.0
   

5. sync the deploy now that we've made a release tag:

   $ pushd ../deploy
   /tmp/project/deploy /tmp/project/develop
   
   $ git reltag sync
   deploying over checked out branch 'master'
   branch head matches desired tag, detaching...
   branch: master
   commit: 37e4ff1c5e78662d2c67d4f88265dd5e00417ebd
   tagname: master-0.0.0
   

6. add another file to the dev repo and release as fix:

   $ pushd
   /tmp/project/develop /tmp/project/deploy
   
   $ touch anotherfile
   $ git add anotherfile
   $ git commit -m 'add another file'
   $ git reltag
   tag master-0.0.1 successfully created, commit message:
   branch: master
   prior: master-0.0.0
   changes: 1
   desc: master-0.0.0-1-gf741b48f96bfbfcbfb9259a6c6c208ef34c3e838
   commit: f741b48f96bfbfcbfb9259a6c6c208ef34c3e838
   prefix: master
   tagname: master-0.0.1
   

7. now that we're detached, we can deploy without args too:

   $ pushd
   /tmp/project/deploy /tmp/project/develop
   
   $ git reltag
   branch: master
   prior: master-0.0.0
   changes: 1
   desc: master-0.0.0-1-gf741b48f96bfbfcbfb9259a6c6c208ef34c3e838
   commit: f741b48f96bfbfcbfb9259a6c6c208ef34c3e838
   prefix: master
   tagname: master-0.0.1
   

8. prepare 1.0, major version update:

   $ pushd
   /tmp/project/develop /tmp/project/deploy
   
   $ echo 'ready for version 1' > README
   $ git add README
   $ git commit -m 'prep readme for GA release'
   $ git reltag major
   tag master-1.0.0 successfully created, commit message:
   branch: master
   prior: master-0.0.1
   changes: 1
   desc: master-0.0.1-1-g84b102c45c5d6b06d9e03bd958f7a13e4f564472
   commit: 84b102c45c5d6b06d9e03bd958f7a13e4f564472
   prefix: master
   tagname: master-1.0.0
   

9. and again the deploy will pull it in with no args:

   $ pushd
   /tmp/project/deploy /tmp/project/develop
   
   $ git reltag
   branch: master
   prior: master-0.0.1
   changes: 1
   desc: master-0.0.1-1-g84b102c45c5d6b06d9e03bd958f7a13e4f564472
   commit: 84b102c45c5d6b06d9e03bd958f7a13e4f564472
   prefix: master
   tagname: master-1.0.0
   

10. found a bug, take the deploy back to prior (working) release:

    $ git reltag prev
    branch: master
    prior: master-0.0.0
    changes: 1
    desc: master-0.0.0-1-gf741b48f96bfbfcbfb9259a6c6c208ef34c3e838
    commit: f741b48f96bfbfcbfb9259a6c6c208ef34c3e838
    prefix: master
    tagname: master-0.0.1
    

and so on.

• allow user-specified tag prefix instead of branch name
• allow suffix string to be specified as well
• forward the gpg verify, avoiding need to trust deploy host's keystore
• mode with less output, maybe just from and to tagname
• configurable fields to go into tag message
• tag message injection from external scripts
• local deploys might better use shared repos ie multi-checkout
• document why we would want to use 'match' subcommand