link-grammar: update to 5.6.1

Version 5.6.1 (27 May 2019)
* Performance improvement (approx 20%) in expressions #882.
* Performance improvement (approx 10%) by disjunct/connectors pools #896.
* Performance improvement (4-10% for English) by faster power-pruning #903.
* Fix a bug in trailing connectors encoding (may cause bad linkages).
* Fix inability to form linkage when first word is disconnected.
* English dict: fix use of quotations with paraphrasing verbs.
* English dict: fix broken usage of "have not".
* Performance improvement (approx 16%) for long sentences. #931
* Performance improvement (approx 20%) for long sentences. #939

Version 5.6.0 (4 January 2019)
* Improve Windows support.
* Fix dict cost reading under user locales with comma decimal separator.
* Support using the pcre2 regex package (configured by default if available).
* Add "-with-regexlib=pcre2|tre|regex|c" to "configure".
* Fix and document building on FreeBSD.
* Major documentation update for building with Cygwin.
* Revise the manpage.
* Remove the experimental Viterbi code.
* Revise the SAT parser cost model to align it with the classic parser.
* Implement a strict check on connector name.
* Major revision of the SWIG interface file; wrap all the library functions.
* Fix linkage_get_disjunct_*() when parse-option display_morphology is true.
* Change library and python-bindings default for display_morphology to true.
* Drastic speedup for long sentences (hash encoding of trailing connectors).
* English dict: Support locative replies/declarations.
* English dict: broaden support for misc paraphrasing verbs.
* English dict: fix relativized paraphrasing.
* English dict: fix comparative-style conjunctions.

(gutteridge)