[Feature Request] Unicode (other special character) support

[tnowacki]

As mentioned in #18, we are very restrictive in our character sets today. We had discussed relaxing this late last year, but made no changes yet. We should open up the character sets and give warnings where we think it might be applicable

[LemonHX]

I will do that! I have a parser written for unicode chars!

[LemonHX]

@tnowacki checkout, I have filtered most useless unicode in my last parser → https://github.com/sap-lang/sap-lang/blob/master/src/utils.rs

[tnowacki]

We probably don't want unicode characters anywhere but in comments. I'll take a look though when we get to this, thanks!