----------------------------
* Bugfixes:
* During conversion between optimized-lookup and other formats, the alphabet
was not being preserved, leading to incorrect behaviour in some cases.
This has been fixed.
* Fix segfaults in hfst-summarize, hfst-disjunct and foma back-end.
* Force ICU, fixes 501.
* Use unique_ptr for input/ouput stream memory allocation (547).
* Improvements:
* hfst-pmatch archives now no longer include or parse redundant alphabets,
which in some cases can be a meaningful size and speed saving.
* Multiple memory leaks fixed.
* Drop support for TR1 standard assuming that C++14 is minimal requirement.
* Drop legacy wrappers for foma and lexc (532).
* Use upstream Foma and by default upstream OpenFST.
* Use C++17, or C++14 with bundled OpenFST.
* Update external links for sfst, foma and flex.
* Add lex/yacc sources to dist (see issue 524).
* Features:
* A new variable in the hfst-pmatch language, "unicode-character-classes",
which causes the use of built-in character sets to be interpreted at
runtime using a unicode library.
* Verbose output from hfst-pmatch2fst has been much improved, providing eg.
a call graph of the process. It also warns about use of pmatch features
that is likely to be incorrect and lead to errors.