Relation Algebra 1.7, for Coq 8.8.2

• compatiblity with Coq 8.8.2 (intermediate versions for Coq 8.6 and 8.7 can be found on github)
• unicode notations (i.e., "x ≡ y", "x ≦ y", "x⋅y")
• support heterogeneous relations on large types (outside [Set])
• [fhrel]: heterogeneous relations between finite types
  (available if coq-mathcomp-ssreflect is present [optional dependency])