TGBA which uses TAA as an intermediate representation. This is a
basic version, optimizations and enhancements will come later.
* src/tgbaalgos/ltl2taa.cc, src/tgbaalgos/ltl2taa.hh: The algortihm.
* src/tgbaalgos/Makefile.am: Adjust.
* src/tgbatest/ltl2tgba: New option: -taa, which uses this new
translation algorithm.
* src/tgbatest/spotlbtt.test: Add ltl2tgba -taa.