Change file-extension

[eydun]

Thank you for building this awesome plugin.

My backup-program wont backup files with the file-extension of ".encrypted". Is it possible to change the file-extension to something else?

[meld-cp]

@GovSat1 mentioned changing the extension too.

It's easy to do and I'm thinking of making the default extension .mdenc

I choose .mdenc because it fits in well with both, the plugin name 'meld encypyt' and the notion of 'markdown encrypted'

[meld-cp]

Added to v2.3.2