delete original after gzipping

[oupala]

There currently only one parameter to set the behavior of the plugin:

• overwrite: true replace files with the compressed version instead of creating a copy with the '.gz' extension
• overwrite: false create a compressed copy version with the '.gz' extension and keep the original file

There could be a good option to add:

• delete-original: true delete original file after creating a compressed copy version with the '.gz' extension

And as delete-original: true would not be compatible with overwrite: true, it could be possible to change the parameter behavior:

• original: keep create a compressed copy version with the '.gz' extension and keep the original file
• original: overwrite replace files with the compressed version instead of creating a copy with the '.gz' extension
• original: delete delete original file after creating a compressed copy version with the '.gz' extension