git-branch-description: remove bashism

Previously this failed when /bin/sh was dash.
git-branch-description: disable pager for showing activity
README.md: indent example blocks by 4 spaces

This makes them show up properly as <pre> blocks in GitHub.
Merge branch 'branch-description-fixups' of https://github.com/jonnylamb/git-branch-tools
git-squash: support Bash from Windows Git

Bash from the Windows Git distribution does not support process
substitution:

    $ git squash
    d:\ext\git-branch-tools\git-squash: cannot make pipe for process substitution: Function not implemented
    d:\ext\git-branch-tools\git-squash: cannot make pipe for process substitution: Function not implemented
    d:\ext\git-branch-tools\git-squash: line 39: <(git log --format="%s" -n $nrefs): ambiguous redirect
    Number to squash in:

Joy. So instead, let's read `git log` straight into the 'refs' array,
and iterate it to produce the menu.
Add a git-for-each helper script

Runs a command on every commit between a refspec.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>