Simplify Custom Line Terminator Handling

[bd82]

The ILexerConfig requires two very similar properties to handle custom line terminators https://sap.github.io/chevrotain/documentation/3_6_1/interfaces/ilexerconfig.html

With a breaking change we can probably only accept a list of strings or charCodes to be used as line terminators and compute the regExp automatically. So only one argument would have to be provided.