Merge branch 'tb/config-type'

Merge branch 'tb/config-type'

The "git config" command uses separate options e.g. "--int",
"--bool", etc. to specify what type the caller wants the value to
be interpreted as.  A new "--type=<typename>" option has been
introduced, which would make it cleaner to define new types.

* tb/config-type:
  builtin/config.c: support `--type=<type>` as preferred alias for `--<type>`
  builtin/config.c: treat type specifiers singularly