[Rewrite] Core config handling

[richrd]

The rewrite needs a config handler and now would be a good time to implement it. The idea is to make it more or less compatible with Sublime Text. The new format wont be backwards compatible with the current version of suplemon (0.1.X). Also editorconfig should be looked into and integrated in the rewrite if possible (http://editorconfig.org/).

A common implementation should be used for both core config and keymap config.

• [ ] Config file format should be similar to sublime text
• [ ] Variable names should be the same as in sublime text
• [ ] Single line comments and trailing commas should be supported (probably use json5)
• [ ] User configs need to be merged on top of defaults
• [ ] Different file formats should be able to have their own specific configs (e.g. tab width 2 for javascript and 4 for python)
• [ ] Defaults can be different from sublime text defaults
• [ ] Not all sublime text options will be implemented