(almost all stdlib doesn't work right now)

Conflicts:
	src/fiber.cr
	src/io/file_descriptor.cr

restore content of prelude to be able to compile the compiler in linux with windows target.

stub regex, iconv for windows

add reference to io/memory due to path io/* expansion and migration to crystal 0.20.3

add (temporal) windows-prelude.cr for easy shrink of samples in windows (require --prelude=empty).

```
# file ./foo.cr
require "./windows-prelude" 
puts "Hello Windows!" 
```

```
$ make # to build the compiler with windows target
$ ./bin/crystal build foo.cr --ll --single-module --cross-compile --target x86_64-windows-gnu --prelude=empty
$ wine /path/to/LLVM-3.9.0/bin/clang.exe  -g3 foo.ll -c -o foo.o
$ /path/to/mxe/usr/bin/x86_64-w64-mingw32.static-gcc -g3 foo.o -o foo.exe -liconv -lkernel32 -lgc -levent -lws2_32
$ wine foo.exe 
Hello Windows!
```

fix src to be able to build the compiler (in linux)

* make file_descriptor.windows.cr not complain. (docs main does a `require "./io/**"`)
* run formatter in several files to make ci happy

* win
* win/...
* win-...
can be built on forks with travis enabled.

allow printing floats. add LibC.memchr

The asynchronous call might return the results synchnourly if the operation can be made without blocking (directly from OS cache). This implies there is need to malloc the overlapped struct, because it need to be alive when the completion notification arrives on the Scheduler. (this will need a mutex)