As part of a push towards more inclusive language, git is reconsidering
using "master" as the default branch name.  As a first step, this
setting will be configurable with the `init.defaultBranch` configuration
option.  Honor this during repository initialization.

During initialization, we will create an initial branch:

1. Using the `initial_head` setting, if specified;
2. Using the `HEAD` configured in a template, if it exists;
3. Using the `init.defaultBranch` configuration option, if it is set; or
4. Using `master` in the absence of additional configuration.