Ethos 0.2.3

This release of Ethos is associated with the 1.3.4 release of the SMT solver cvc5.

• The command declare-parameterized-const now forbids return types that contain parameters with non-ground type.
• Updates to the external plugin interface.
• The identifier Type is no longer treated as a keyword in proofs and reference files.
• The command declare-sort is now allowed in proof files.
• The builtin eo::to_str no longer prints rationals, decimals, or bitvectors. It now only evaluates on strings and numeral code points.
• Adds support for an attribute :is_eq to test whether a defined term is equal to another.
• Fixes a bug where the character code point \u{30000} was incorrectly
  treated as a valid code point.
• Fixes issue in the parser which did not guard for overflow of 32 bit unsigned
  values.
• Fixes an issue where non-ground nil terminators would not be properly computed for list construction operators with types where the element type is different from the return type of the operator.
• Fixes for evaluation of :left-assoc-nil and :left-assoc-non-singleton-nil operators.
• Variables (eo::var s T) are now considered ordinary terms, which are hence allowed in patterns.
• Fixes the implementation of eo::list_minclude, which had considered the arguments in opposite order.