fix appveyor link in readme
msvs: also define _DEBUG for debug builds
[appveyor] more debug flags
[appveyor][gyp] correct msvs_settings usage
customize release builds
[gyp][windows] add exception handling/rtti
use numeric values in valid range to avoid overflowing
Removed wrong comments.
Removed test case.

After the changes to it, this test doesn't test any more what it was supposed to test (that implicit conversion is done to first convertible type and not first type that can hold the value). So it can be removed now because it tests the same thing as the test above it.
allow explicit un-initilised variant ctor

```c++
util::variant<int, double, std::string> var(util::no_init());
var.valid(); // false
util::variant<int, double, std::string>(util::no_init()).get_type_index() == util::detail::invalid_value; // true
```
add boost::variant compatible accessors
more verbose output to test script
variant : make operator<< stricter to avoid unexpected instantiations
Add details on advantages of Mapbox variant
remove unneeded header
less debug info in release mode
rough cut of an optional type
add operator* and a static assert against reference types
Merge pull request #30 from DennisOSRM/optional

rough cut of an optional type
remove some whitespace