fix(Types): Move distinct types into distinct identifiers

This allows types to be collected; prior to this commit they
   were conflicting from different modules.

   Uses this fix to extend sqrt to bigint, with the convention
   that it is undefined for non-perfect squares when 'predictable'
   is false and is the "best" approximation to the square root when
   'predictable' is true. Furthermore, for negative bigints, you might
   get a Gaussian integer when predictable is false; or you will just get
   your argument back when 'predictable' is true because what other
   bigint could you give back for a negative bigint?

   Also had to modify tests on the sign in sqrt(Complex) and add functions
   'zero' and 'one' to get types to match, as expected in #27.

   Adds numerous tests.

   Resolves #26.
   Resolves #27.

test/complex/_all.mjs

@@ -9,6 +9,9 @@ describe('complex', () => {
       assert.deepStrictEqual(
          math.sqrt(math.complex(0,1)),
          math.complex(math.sqrt(0.5), math.sqrt(0.5)))
+      assert.deepStrictEqual(
+         math.sqrt(math.complex(5, 12)),
+         math.complex(3, 2))
       math.config.predictable = true
       assert.deepStrictEqual(math.sqrt(math.complex(1,0)), math.complex(1,0))
       assert.deepStrictEqual(