Add enum class to docs and remove bools from examples

Author: mborland

doc/modules/ROOT/pages/basics.adoc

@@ -16,21 +16,33 @@ Every decimal type can be constructed in a few ways:
 
 [source, c++]
 ----
+namespace boost {
+namespace decimal {
+
+enum class construction_sign
+{
+    negative,
+    positive
+};
+
 template <typename UnsignedInteger, typename Integer>
-constexpr decimal32_t(UnsignedInteger coefficient, Integer exponent, bool is_negative = false) noexcept;
+constexpr decimal32_t(UnsignedInteger coefficient, Integer exponent, construction_sign resultant_sign = construction_sign::positive) noexcept;
 
 template <typename SignedInteger, typename Integer>
 constexpr decimal32_t(SignedInteger coefficient, Integer exponent) noexcept;
+
+} // namespace decimal
+} // namespace boost
 ----
 
 As you can see you are either allowed to pass a signed integer, or specify the signedness of the resulting number, but not both.
-This is designed to reduce confusion (e.g. what would be the resulting sign of `{-3, 0, true}`?)
+This is designed to reduce confusion (e.g. what would be the resulting sign of `{-3, 0, construction_sign::negative}`?)
 
 [souce, c++]
 ----
 boost::decimal::decimal32_t a {1, 1};           // constructs 1e1 = 10
 boost::decimal::decimal32_t b {-2, -1};         // constructs -2e-2 or -0.2
-boost::decimal::decimal32_t c {2U, -1, true};   // also constructs -2e-1 or -0.2 (Note: The coefficient must be an unsigned type)
+boost::decimal::decimal32_t c {2U, -1, construction_sign::negative};   // also constructs -2e-1 or -0.2 (Note: The coefficient must be an unsigned type)
 boost::decimal::decimal32_t e {5, 5};           // constructs 5x10^5
 boost::decimal::decimal32_t f {1234, -3}        // constructs 1.234 or 1234x10^-3
 ----

doc/modules/ROOT/pages/examples.adoc

@@ -26,7 +26,7 @@ int main()
 
     std::cout << sum << std::endl; // prints 0.3
 
-    const boost::decimal::decimal32_t neg_a {2, -1, true}; // Constructs the number -0.2
+    const boost::decimal::decimal32_t neg_a {2, -1, construction_sign::negative}; // Constructs the number -0.2
 
     sum += neg_a;