replaces canvg by of (HTML) canvas methods

[sverweij]

• Pros:
  • The drawImage() method is more reliable than canvg (or any-vector-on-a-canvas package for that matter) as it's doing platform native rendering
  • two dependencies less (canvg and the bower development dependency)
• Con: a tiny bit more complexity in thee raster export functions because
  • it has to determine svg height and width, to resize the canvas
  • the stuff is synchronous, so we need a promise or callback (chose the latter)
  • the drawImage() approach probably won't work in elderly browsers that lack proper svg support, but these won't run mscgen_js properly anyway.

[codecov-io]

@@            master    #227   diff @@
======================================
  Files            4       4       
  Stmts           87      87       
  Branches         0       0       
  Methods          0       0       
======================================
  Hit             87      87       
  Partial          0       0       
  Missed           0       0       

Review entire Coverage Diff as of 5a58328

Powered by Codecov. Updated on successful CI builds.