#12 tweek css
#12 change image src to svg
#13 save svg to external files
#13 tweak saving
when file is saved:
- comment out diagram blocks
- add markdown syntax image

when file is opened:
- comment in diagram blocks
- remove markdown syntax image
Merge branch 'feature/#12' into develop
Merge branch 'feature/#13' into develop
#14 save window size
#14 support for fullscreen
Merge branch 'feature/#14' into develop
#15 change version number to 1.2.0
#15 change README.md
Merge branch 'release/1.2.0' into develop