1.8.4; soversion=20

Merge pull request open-source-parsers#655 from cdunn2001/fix-649

Fixes open-source-parsers#649
Fixes open-source-parsers#654

Merge pull request open-source-parsers#652 from cdunn2001/meson-not-s…

…cons

Meson not scons; 1.8.2<-1.8.1

Require cmake>=3.1

Plus some other build-related changes. I don't think there is anything
functionally different from 1.7.7, or even any binary incompatibilities, but
the cmake change is significant.

1.7.6 <- 1.7.5

1.7.5 <- 1.7.4

1.7.4 <- 1.7.3

Merge pull request open-source-parsers#490 from open-source-parsers/n…

…ull-singleton

Use a Myers Singleton for null