No FunSQL definitions for operators ≥ or ≤

[AshlinHarris]

FunSQL requires the <= and >= operators for comparison, as there are no methods defined for ≥ or ≤.

Example:

julia> using FunSQL

julia> @funsql begin
           from(person)
           filter(1930 ≤ year_of_birth ≤ 1940)
       end
ERROR: UndefVarError: `funsql_≤` not defined
Stacktrace:
 [1] top-level scope
   @ REPL[2]:3

[xitology]

Added in #67