Update License to SPDX. Switch to CMake, run tests, and ship CMake files. Update from 2.8.1 to 2.8.3, with some bug fixes:

2.8.2

• Fixed parse tree node generation to correctly remove intermediate nodes.

2.8.3

• Fixed excessive read-ahead with incremental inputs.
• Added state manipulators remove_first_state, remove_last_states, rotate_states_right, rotate_states_left, and reverse_states to contrib.
• Reduced the number of intermediate parse tree nodes.