Implement blackbox in Golang (#250)

* Initial release

docs/full-command-list.md

@@ -0,0 +1,34 @@
+Blackbox Command List
+=====================
+
+## Global Flags
+### `--vcs`
+### `--crypto`
+### `--config`
+### `--team`
+### `--editor`
+### `--umask`
+### `--debug`
+### `--help`
+### `--help`
+### `--version`
+## User Commands
+### `blackbox decrypt`
+### `blackbox encrypt`
+### `blackbox edit`
+### `blackbox cat`
+### `blackbox diff`
+### `blackbox shred`
+### `blackbox help`
+## User Commands
+### `blackbox init`
+### `blackbox admin`
+### `blackbox file`
+### `blackbox status`
+### `blackbox reencrypt`
+## Debug
+### `blackbox info`
+## Integration Test (secret menu)
+### `blackbox testing_init`
+
+TODO(tlim): Can we automatically generate this?  The data is all in cli.go