compose manpage out of rsts from gh-pages-gen

[pskocik]

uses the rsts moved from gh-pages-gen to compose the manpage

[skvadrik]

It's almost ok, except that a couple of Travis CI builds failed: https://travis-ci.org/skvadrik/re2c/builds/220255998

I believe that failures are caused by include paths in doc/manpage.rst: they should be relative to top source directory, that is, doc/manual/options/options_list.rst instead of manual/options/options_list.rst an so on.

[skvadrik]

I'll pull your patch and add a fix on top of it.

[skvadrik]

Pulled your patch; fixed paths to be relative to @top_srcdir@ (see e5c74f4). Now all checks pass: https://travis-ci.org/skvadrik/re2c.

Thanks!

[pskocik]

Thanks for fixing it. I should've had it run through travis too.

I named the fragments rst_ to prevent them from being picked up by the build system for rst to html conversion.