Iterative (chunked) input processing

Remove now unneeded workaround

The workaround would now cause build failures in Appveyor as seem to
have pre-emptively applied it to their environments.

I'm not too happy about their handling of the issue. Seems fiddly.

Anyway this commit is now required to build on Appveyor.

Add workaround for VS2015 so that appveyor works

It seems Appveyor's images have been changed. The builds could not
find standard library headers anymore.

It seems to be an interaction between MS' scripts and the Windows
Driver Kit that is installed there.

One way to disable this interaction is to rename the `wdf` folder to
some other name.

See:
- http://stackoverflow.com/questions/31862627/vs2015-cl-cant-find-crt-libs-stido-h-ctype-h-etc-when-building-on-command-l
- http://help.appveyor.com/discussions/problems/3062-problem-with-new-updates-visual-studio-2015-and-cmake
- https://github.com/appveyor/ci/issues/414

Fix two context-free backend bugs

add a missing end-of-input check in the LL(k) backend

Platform compilation improvement (windows port)

We have now again two functions called h_platform_vasprintf and
h_platform_asprintf. On windows they are implemented in terms of vsnprint
and the like. On BSD/GNU libraries we use the supplied vasprintf and
asprintf.

Since the block of code has been disabled anyway and is not very
portable, we introduce a define to control both the include
and the code.