Add support for transparent editing

[szaffarano]

I think that a good enhancement could be to allow transparent editing like gnupg vim plugin. If you open a file with either .gpg or .asc extension, then the plugin encrypt and decrypt its content automatically and transparently.

[safijari]

Was going to discuss using gpg with colleagues that use vscode (I use emacs) and just realized none of the gpg extensions in vscode do this. Darn.