Refactor bigints, add int and float conv functions

Added functions to convert from/to ints/floats. Floats are converted
according to basic Steele&White algorithm (without speedup).

src/String/Core.c

@@ -0,0 +1,21 @@
+#include <BH/String.h>
+#include <stdlib.h>
+#include <string.h>
+
+
+void BH_StringFree(char *string)
+{
+    free(string);
+}
+
+
+char *BH_StringCopy(const char *string)
+{
+    char *result;
+    
+    result = malloc(strlen(string) + 1);
+    if (result)
+        strcpy(result, string);
+
+    return result;
+}