[isabelle-dev] Update of Isabelle/jEdit manual: screenshots

[Makarius]

In Isabelle/2337a6bc5e41, I have updated the screenshots of the
Isabelle/jEdit manual, using a macMini with current Mojave and a regular
UHD display, but only a small portion of the screen; there is one
screenshot with Linux Ubuntu Budgie that uses the full pixel-range of it.

The visual appearance on my 3 test displays is as follows:

  * Samsung UHD 28" (2017, 330 EUR): better than before in every respect

  * Sony Vaio HD 17" (2013): pretty good, better font shapes than before

  * Iiyama HD 21" (2019, 80 EUR): quite bad (also for native macOS
applications)

My overall conclusion: OpenJDK 11 is more honest in the rendering, i.e.
a good display gives good results, a bad display gives bad results.


I will work on the text of the manual later: with updated notes about
high-quality vs. low-quality displays; also about font hinting vs.
non-hinting.


	Makarius