Adds export to PNG and export to JPEG

[sverweij]

This adds two commands to svg-preview: svg-preview:export-to-png and svg-preview:export-to-jpeg. When triggered, they execute the following actions (added to lib/svg-preview-view.coffee in the exportTo function):

• Convert the current svg to the specified raster format (respectively png or jpeg).
  • The canvas API toDataURL function takes care of the conversion. Implementation details in lib/svg-to-raster.coffee.
• Open a Save As dialog and (after the user closes the Save As dialog) saves the raster graphic to the specified location
• Opens the raster graphic

As a first proposal this change binds the commands to context menu items in the previewer (menus/svg-preview.cson)

Notes:

• It uses fs-plus for saving the raster graphics. fs-plus already was a development dependency - this change promotes it to a regular dependency.
• Both fs-plus and svg-to-raster are only loaded when the conversion actions are triggered for the first time, in order for them not to impact package load time.
• Specs/ tests for both commands in spec/svg-preview-spec.coffee

[josa42]

👍 That's awesome, thank you. I am sorry to ask, but could you convert this to ES6? I planned to mereg the convert-to-js branch for the next release.

[sverweij]

I anticipated this - you'll get a new PR based on the convert-to-js branch in the coming days.

[josa42]

@sverweij Thank you, sorry for the extra work.