Avoid stutter. Fixes #55
* Reflect actual slice type in TreeFromMap * Fix writeTo for slices tomlValues Fixes #143
* Use String() of key if it exists during TreeFromMap
* Make TreeFromMap reflect to construct tree * Fix wording of invalid value type in writeTo Fixes #138, #139, #134 ⚠️ TreeFromMap signature changed to `TreeFromMap(map[string]interface{}) (*TomlTree, error)`