Fixed issue with idea-multimarkdown.

- JavaFX does not support lookbehind
 - (?) It also appears that named regex groups are also unsupported for both mermaid and javafx

Update:
 - Fixed an issue where setLogLevel did not properly handle 'named' log levels
 - Backwards compatibility should be preserved, any/all %%{...}%% directives will be correctly processed by the grammar and properly ignored for any/all graph types that do not support them.

 - Multiline directives will render an error (as they should) if they are not accounted for in the .jison grammar

src/mermaidAPI.js

@@ -104,7 +104,6 @@ const config = {
    */
   theme: 'default',
   themeCSS: undefined,
-  multilineDirectives: false,
   /* **maxTextSize** - The maximum allowed size of the users text diamgram */
   maxTextSize: 50000,