Exception refactoring

Fixes #90 
- [x] Create an `Exception` interface
- [x] Refactore existing exceptions and deprecate old ones
- [x] Create new exception to throw instead of the ones from STL or Symfony
- [x] Update tests to use new exception class names (works without that because it's BC :v:)
- [x] Update docblocks with the right version of deprecation
- [x] Update docs
always include `$code = 0` and `\Exception $previous = null` as arguments to exception (these are also in the main exception class).