[ITA] cygwin-doc

[Jon TURNEY]

As invited [1], I shall adopt the cygwin-doc package.

wget="wget -rxnH --cut-dirs=4 
http://www.dronecode.org.uk/cygwin/x86_64/release/cygwin-doc/"
$wget/cygwin-doc-1.7.35-1.tar.xz
$wget/cygwin-doc-1.7.35-1-src.tar.xz

In this incarnation, it contains:

* newlib libc and libm .info documentation
* man pages for newlib functions, generated from .info
* intro.1 and intro.3 man pages for Cygwin, handwritten
* man pages for Cygwin utilities, generated from the DocBook XML
* man pages Cygwin-specific functions, generated from the DocBook XML
* Cygwin User's Guide and API reference texinfo, generated from the 
DocBook XML

I have reworked the scripts as a series of patches which are applied to 
the cygwin source by a cygport script, which should make it easier to 
build and keep up to date.  Some of those patches are possibly even 
suitable for upstreaming.

I've also made a few adjustments to update and improve the conversion 
scripts, so the output should be at least as good as it was previously, 
although there are still some flaws in the automatically converted 
documents.

[1] https://cygwin.com/ml/cygwin-developers/2014-06/msg00000.html