CMake improvements

initial fixes for building kj/main.c++ utilities on mingw

Remove '-d' flag from call to atos(1)

That is to say, whereas previously we would extend capnp::typeId<T>() to a new type by declaring a specialization of it for that type, now we instead have the type contain a nested class called _capnpPrivate which contains a `typeId` constant.

This is necessary because it is impossible to specialize a template for a type which is itself nested inside a template type. E.g. it's impossible to write a specialization `template <typename T> typeId<Foo<T>::Bar>()`; C++ simply doesn't support this. But with generics, Cap'n Proto will allow types to be nested inside templates, so we need this to work.

atos(1) doesn't actually have a '-d' flag, but its inclusion was
innocuous (and suppressed a warning) until OS X 10.10.

1) Apparently mixing member defaults and initializer lists is a C++14 thing.
2) My test script compiles with -Werror which errors out on calls to now-deprecated getDependency().

More refactoring is needed, but this at least makes "using" aliases work correctly with generics.

This function now (on windows):
* converts \n to \r\n (for both file and console outputs)
* when the output is redirected to a file, uses WriteFile with utf-8 output
* when the output will appear on a console, uses WriteConsole with utf-16 output instead

add fix for older cmake versions

Add initial cmake build support

* Move binaries into the bin directory and libs into the lib directory in the output
* Make sure the actual binary output file of capnp-tool is just capnp
* Remove need for deprecated cmake get_property function