1.8.1

Bug fixes 1.8.1 milestone:

• [null ptr when extracting "the" rule. bug comp:grammar-editor](https://github.com/antlr/intellij-plugin-v4/issues/254]
• [right click doesn't select rule for testing that rule bug comp:GUI](https://github.com/antlr/intellij-plugin-v4/issues/251]
• [Icon looks blurry on Retina display enhancement](https://github.com/antlr/intellij-plugin-v4/issues/244]
• [antlr can't process Grammar.g4 bug](https://github.com/antlr/intellij-plugin-v4/issues/241]
• null ptr when looking at profiler I think w/o start rule or something bug comp:preview
• support for empty String ("") in locals

Updates ANTLR 4.5.3 from 4.5.1

Improvements 1.8.1 milestone