Remove hand written conversion code and replace with stdlib features.

With C++11 the stdlib gains:

- `std::stoi` function family to convert from `std::string` to integral type

- `std::to_string` to convert from number types to `std::string`

The only reason for hand-writing the conversion code therefore is
performance. I benchmarked an `osrm-extract` with the hand-written code
against one with the stdlib conversion features and could not find any
significant difference (we switch back and forth between C++ and Lua,
shaving off a few us in conversion doesn't gain us much).

Formatting arithmetic types in the default format with given precision
requires streams, but is doable in a few lines of idiomatic stdlib code.

For this, there is now the following function template available:

    template <Arithmetic T, int Precision = 6>
    inline std::string to_string_with_precision(const T);

that requires integral or floating point types and returns a formatted
string in the defaukt format with the given precision applied.

In addition this completely rips out Boost.Spirit from the `casts.hpp`
header, resulting in faster compile times.

Boom!

References:

- http://en.cppreference.com/w/cpp/string/basic_string/stol
- http://en.cppreference.com/w/cpp/string/basic_string/to_string
- http://www.kumobius.com/2013/08/c-string-to-int/

extractor/extraction_helper_functions.hpp

@@ -37,6 +37,7 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <boost/regex.hpp>
 
 #include <limits>
+#include <string>
 
 bool simple_duration_is_valid(const std::string &s)
 {
@@ -89,18 +90,18 @@ unsigned parseDuration(const std::string &s)
         {
             if (1 == result.size())
             {
-                minutes = cast::string_to_int(result[0]);
+                minutes = std::stoul(result[0]);
             }
             if (2 == result.size())
             {
-                minutes = cast::string_to_int(result[1]);
-                hours = cast::string_to_int(result[0]);
+                minutes = std::stoul(result[1]);
+                hours = std::stoul(result[0]);
             }
             if (3 == result.size())
             {
-                seconds = cast::string_to_int(result[2]);
-                minutes = cast::string_to_int(result[1]);
-                hours = cast::string_to_int(result[0]);
+                seconds = std::stoul(result[2]);
+                minutes = std::stoul(result[1]);
+                hours = std::stoul(result[0]);
             }
             return (3600 * hours + 60 * minutes + seconds);
         }