buildsystem: drop custom buildconf script, rely on autoreconf (#224)

Notes:
The buildconf script is currently required, because we need to copy a
header around, because it is used both from the library and the examples
sources.

However, having a custom 'buildconf'-like script is not needed if we can
ensure that the header exists by the time it is needed. For that, we can
just append the src/ directory to the headers search path for the
examples.

And then it means we no longer need to generate the same header twice,
so we remove the second one from configure.ac.

Now, we can just call "autoreconf -fi" to generate the autotools files,
instead of relying on the canned sequence in "buildconf", since
autoreconf has now long known what to do at the correct moment (future
versions of autotools, automake, autopoint, autoheader etc... may
require an other ordering, or other intermediate steps, etc...).

Eventually, get rid of buildconf now it is no longer needed. In fact, we
really keep it for legacy, but have it just call autoreconf (and print a
nice user-friendly warning). Don't include it in the release tarballs,
though.

Update doc, gitignore, and travis-CI jobs accordingly.

Credit:
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Sam Voss <sam.voss@rockwellcollins.com>

example/.gitignore

@@ -21,8 +21,6 @@ config.h.in
 ssh2_exec
 ssh2_agent
 ssh2_agent_forwarding
-libssh2_config.h
-libssh2_config.h.in
 stamp-h2
 sftp_append
 sftp_write_sliding

example/Makefile.am

@@ -13,5 +13,5 @@ if HAVE_SYS_UN_H
 noinst_PROGRAMS += x11
 endif
 
-AM_CPPFLAGS = -I$(top_srcdir)/include -I$(top_builddir)/example
+AM_CPPFLAGS = -I$(top_srcdir)/include -I$(top_builddir)/example -I../src
 LDADD = $(top_builddir)/src/libssh2.la