add support for enumeration types in debug_info

[abroooo]

Is your feature request related to a problem? Please describe.
The functions LLVMDIBuilderCreateEnumerationType and LLVMDIBuilderCreateEnumerator are not implemented in inkwell. They are needed to create debug information for enumerations and enumerators.

Describe the solution you'd like
Extend the debug_info.rs to support creating enumeration types and enumerators.

I can provide a PR soon to add support for this.