style: Refactor gh_asset_erase to nicely report status messages
style: Refactor gh_asset_erase to nicely report status messages

For example, without verbose:

```
$ githubrelease asset jcfr/sandbox erase nightly "*cp35*" --keep-pattern "*win*" --dry-run
deleting 'nightly' release asset(s) (matched: 4, matched-and-keep: 2, not-matched: 12):
  deleting sandbox-2.0.0.dev20170105-cp35-cp35m-macosx_10_11_x86_64.whl
  deleting sandbox-2.0.0.dev20170105-cp35-cp35m-manylinux1_x86_64.whl
```

and with verbose:

```
$ githubrelease asset jcfr/sandbox erase nightly "*cp35*" --keep-pattern "*win*" --dry-run --verbose
deleting 'nightly' release asset(s) (matched: 4, matched-but-keep: 2, not-matched: 12):
  deleting sandbox-2.0.0.dev20170105-cp35-cp35m-macosx_10_11_x86_64.whl
  deleting sandbox-2.0.0.dev20170105-cp35-cp35m-manylinux1_x86_64.whl
  skipping sandbox-2.0.0.dev20170105-cp35-cp35m-win32.whl (match keep_pattern '*win*')
  skipping sandbox-2.0.0.dev20170105-cp35-cp35m-win_amd64.whl (match keep_pattern '*win*')

  assets NOT matching selection pattern [*cp35*]:
    sandbox-2.0.0.dev20170105-cp34-cp34m-win_amd64.whl
    sandbox-2.0.0.dev20170105-cp36-cp36m-win32.whl
    sandbox-2.0.0.dev20170105-cp27-cp27m-manylinux1_x86_64.whl
    sandbox-2.0.0.dev20170105-cp36-cp36m-win_amd64.whl
    sandbox-2.0.0.dev20170105-cp34-cp34m-manylinux1_x86_64.whl
    sandbox-2.0.0.dev20170105-cp34-cp34m-macosx_10_11_x86_64.whl
    sandbox-2.0.0.dev20170105-cp27-cp27m-win32.whl
    sandbox-2.0.0.dev20170105-cp34-cp34m-win32.whl
    sandbox-2.0.0.dev20170105-cp27-cp27m-macosx_10_11_x86_64.whl
    sandbox-2.0.0.dev20170105-cp36-cp36m-manylinux1_x86_64.whl
    sandbox-2.0.0.dev20170105-cp36-cp36m-macosx_10_11_x86_64.whl
    sandbox-2.0.0.dev20170105-cp27-cp27m-win_amd64.whl
```

j0057/github-release,j0057/github-release