Completely rip out Boost's Spirit / Karma for casting.

This rips out the Bost Spirit / Karma conversion code, using the stdlib
and lightweight alternatives instead.

The main benefit is an immense decrease in compilation times, for every
translation unit that requires the `util/cast.hpp` header.

Note: compared to the version before, there is a minor change in
behavior: the double `-0` was printed as `0` before and is now printed
as `-0`. This comes from the IEE754 standard, specifying signed zeros,
that is `+0` and `-0`. Interesting for us: JavaScript uses IEE754,
resulting in no breakage if used in arithmetic.

Small test case, left hand side was before, right hand side is now:

    $ ./a.out
    -1.123457 vs -1.123457
    -1 vs -1
    -1.3 vs -1.3
    0 vs -0
    0 vs 0
    0 vs 0
    1.3 vs 1.3
    1.123457 vs 1.123457

References:

- https://en.wikipedia.org/wiki/Signed_zero
- http://www.boost.org/doc/libs/1_59_0/doc/html/boost/algorithm/trim_right_if.html
- http://www.boost.org/doc/libs/1_59_0/doc/html/boost/algorithm/is_any_of.html

util/cast.hpp

@@ -33,6 +33,9 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <iomanip>
 #include <type_traits>
 
+#include <boost/algorithm/string/classification.hpp>
+#include <boost/algorithm/string/trim.hpp>
+
 namespace cast
 {
 template <typename Enumeration>
@@ -47,8 +50,19 @@ template <typename T, int Precision = 6> inline std::string to_string_with_preci
     static_assert(std::is_arithmetic<T>::value, "integral or floating point type required");
 
     std::ostringstream out;
-    out << std::setprecision(Precision) << x;
-    return out.str();
+    out << std::fixed << std::setprecision(Precision) << x;
+    auto rv = out.str();
+
+    // Javascript has no separation of float / int, digits without a '.' are integral typed
+    // X.Y.0 -> X.Y
+    // X.0 -> X
+    boost::trim_right_if(rv, boost::is_any_of("0"));
+    boost::trim_right_if(rv, boost::is_any_of("."));
+    // Note:
+    //  - assumes the locale to use '.' as digit separator
+    //  - this is not identical to:  trim_right_if(rv, is_any_of('0 .'))
+
+    return rv;
 }
 }