Gradle Build and temporary file handling

• Plugin is now build using the Gradle and gradle-intellij-plugin
  This should make contributing and releasing easier. Thanks Jiawen Geng!
• Asciidoctor's temporary files are now created in a temporary folder per opened document. Thanks @agorges!

Fixed code/preview sync for nested HTML (i.e. NOTE)

• Improved handling of trailing spaces in syntax highlighting.
• Fixed code/preview sync for nested HTML (i.e. NOTE)

Updated block parsing

Updated block parsing to support two styles of headings.
Block starts and ends are needed to be aligned in length and shape when parsed.

(see #146)

Improved JavaFX darcula support

Improved darcula support for JavaFX. More block types are using proper dark background and light text colors.

Preview theme in settings (light vs. darcula)

Theme in preview can be switched from light to darcula independent of IDE theme

Better Linux/MacOS Support for JavaFX preview

• Handling of Linux and MacOS file names for image preview in JavaFX

Darcula and Click-on-Preview

• Added darcula theme for JavaFX preview
• Clicking on JavaFX preview will set cursor position in editor (thanks to @kastork for the idea)

Fighting hanging JavaFX panels on MacOS

setScene now called from FxThread instead of AWT thread to avoid blocking GUI on MacOS (#133)

Finalizing JavaFX scrolling functionality

• Initialization message appears only during initialization
• No error message if user switches to a setup where JavaFX preview is no longer available.

JavaFX autoscrolling preview #3 - detect 64bit JVM on Mac

• fixed detection of Mac 64 JVM to be able to activate JavaFX preview
• click-on-url for JavaFX improved, when slow-loading external images are referenced