* Improve default toml encoder for complex types
The default toml encoder failed for more complex structs, as certain
edge cases were not covered. This commit attempts to fix this by adding
additional handling for these edge cases.
* Improve map encoding
Since maps currently only support keys that have a string
representation, we can utilize this during map encoding.
* Add test cases for toml encoding
Added test cases for toml encoding of complex nested structs and structs
that contain maps.
* Add additional test cases
