Dockhand

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- Isolate all git functionality, so as to create pluggable Source Control wrappers.

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- Fix issue when images are built, but not in git.

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- Support .dockerignore files on Py3k
- shipwright 'build' sub-command is no-longer optional
- Support extra tags with '-t'
- Continue the build on failure, defer sys.exit until the end of the build.
- Support shor names in TARGETS.

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- Removed curry decorator.
- Removed shipwright.version module.
- Removed purge command.
- Fixed various Python 3 bugs.

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- First version of dockhand that can be installed from PyPI