Support Enum

[horoshenkiy]

Hello!

Thanks for your contribution to open source. I and my team are waiting for this library for a long time. We have self-made library which using RTTR for config loading but we think this have problems.

Your library is more comfortable. It's great!
But we can't find methods for using enums. Maybe can you help us?

[netcan]

for history reason, before I developped this library, our project needs to manually maintain the mapping table of enum and string, so after I developped the library, we don't need to do mapping anymore(just manually maintain it)

my sugguestion is your config file using the enum string, and temporarily build the enum table, I would consider enumeration support later.