bash 3.2 for bashup tests

This is a docker image for compatibility-testing bashup and dirtsimple projects with bash 3.2. It adds the following modules to the official bash:3.2 image:

• less and ncurses (for paging test results and cutting them to the current screen size)
• py-pygments (for colorizing the test diffs)
• python (for running cram)
• git (to fetch dependencies)
• entr (to support devkit's watch command)
• jq, yaml2json and py-yaml (for jqmd)
• php5 as php (for testing imposer)
• go and musl-dev (for building go-based dependencies)
• shellcheck (for linting shell scripts)

To use it in your .devkit-based projects, just dk use: bash32 in your .dkrc. You can then run any standard devkit commands via dk bash32 command..., e.g. dk bash32 test, dk bash32 watch, dk bash32 console, etc.