1.0.b20: Several improvements to UI and supported files.

New features:
- new simple UI.
- support for .strings, .ini and .cfg files.
- support for .xib and .storyboard files as XML.
- preview can show custom source file.
- better support for standard preprocessor for many file format (if you have previously customized the preprocessor for some formats please check if it require to add the placeholder $targetHL).
- highlight updated to 3.57.
Bugfix:
- rust file extension.
- settings migration.