libnyth 0.2.0

Changes from 0.1.0:

- The implemented Nyth version is now 0.3.0.
- struct nyth_position has been renamed to struct nyth_location.
- enum nyth_error was removed; errors are represented by their
  descriptions now.
- Functions that can fail return a bool now.
- I/O abstractions have been removed; FILE is used instead.
- NYTH_EVENT_NONE has been removed;
- Collection event types have been been replaced with
  NYTH_EVENT_COLLECTION and NYTH_EVENT_END.
- enum nyth_collection is introducted to represent the type of
  a collection.
- The length field of struct nyth_scalar was renamed to len.