Changelog for what4-1.1

1.1 (Febuary 2021)

Use multithread-safe storage primitive for configuration options, and clarify single-threaded use assumptions for other data structures.
Fix issue #63, which caused traversals to include the bodies of defined functions at call sites, which yielded confusing results.
Add concrete evaluation and constant folding for floating-point operations via the libBF library.
Add min and max operations for integers and reals to the expression interface.
Remove BaseNatType from the set of base types. There were bugs relating to having nat types appear in structs, arrays and functions that were difficult to fix. Natural number values are still avaliable as scalars (where they are repesented by integers with nonzero assumptions) via the SymNat type.
Support for exporting What4 terms to Verilog syntax.
Various documentation fixes and improvements.
Test coverage improvements.
Switch to use the prettyprinter package for user-facing output.