Case-insensetive language

[ghaith]

Is your feature request related to a problem? Please describe.
The standard does not set any casing rules for the language. For compatibility reasons, we should allow case differences in the keyword and reference called.
Optionally we should make this enabled via a flag.

Describe the solution you'd like
When looking for references, we should ignore the case that the reference is written in.
When parsing keywords, we should support all versions.