Add documentation in Texinfo format.

* configure.ac: Add `doc/Makefile' to `AC_CONFIG_FILES'.
* Makefile.am (SUBDIRS): Add `doc' directory.
* doc/Makefile.am: New file.
* doc/api-auth.texi, doc/api-channels.texi, doc/api-keys.texi,
  doc/api-messages.texi, doc/api-servers.texi,
  doc/api-sessions.texi, doc/api-version.texi, doc/fdl.texi,
  doc/guile-ssh.texi, doc/indices.texi, doc/version.texi: New file.
Merge branch 'master' into documentation

Conflicts:
	ChangeLog
doc/api-{sessions,servers}.texi: Improve documentation.

* doc/api-sessions.texi (Sessions): Improve description of
  `session-set!' procedure.
* doc/api-servers.texi (Servers): Improve description of
  `server-set!' procedure.
* doc/version.texi: Update.
doc/*: Improve the documentation.

* doc/api-auth.texi, api-channels.texi, api-keys.texi,
  api-servers.texi, api-sessions.texi, api-version.texi,
  guile-ssh.texi: Improve.
doc/guile-ssh.texi: Fix integration with Info system.

* doc/guile-ssh.texi: Fix the top-level node of the documentation
  so now it integrates nicely into Info system.
doc/api-{servers,messages}.texi: Improve documentation.

* doc/api-servers.texi (Servers): Add reference to `Messages' node.
* doc/api-messages.texi (Message Handling): Add reference to
  `Parsing of Requests' node.
  (Parsing of Requests): Improve documentation for request parsers.
doc/guile-ssh.texi (Acknowledgments): Add new node.

* doc/guile-ssh.texi (Acknowledgments): Add new node.
  (Top): Add `Acknowledgments'.
doc/guile-ssh.texi (Examples): Update.

* doc/guile-ssh.texi (Examples): Add information about installed
  examples.
guile-ssh.texi: Remove `Preface'.  Add `installation'.

* doc/guile-ssh.texi: Remove `Preface' node.
  (Installation): New node.
doc/guile-ssh.texi (Top): Add `Concept Index'.

* doc/api-version.texi (Version): Update concepts.
* doc/api-sessions.texi (Sessions): Likewise.
* doc/api-messages.texi (Messages, Parsing of Requests): Likewise.
* doc/api-channels.texi (Channels): Likewise.
* doc/api-auth.texi (Auth): Likewise.
* doc/guile-ssh.texi (Top): Add `Concept Index'.
* doc/indices.texi (Concept Index): New node.
api-channels.texi (Channels): Add brief description.  Update.

* doc/api-channels.texi (Channels): Add brief description of the
  channel type.  Add example of `channel-request-exec' usage.  Add
  description of `channel-set-stream!' and `channel-get-stream'
  procedure.
doc/api-servers.texi: Add copyright notice.
session-func.c (session_options): Remove duplicated options.

* src/session-func.c (session_options): Remove duplicates that are
  existed for some options: `port-str', `log-verbosity-str',
  `add-identity'.
  (set_option): Likewise.
* NEWS: Update.
Merge branch 'master' into tests-implementation

Conflicts:
	ChangeLog
tests/server.scm: `server-set!', check `hostkey' option.

* tests/server.scm ("server-set!, valid values"): Check `hostkey'
  option.
  ("server-set!, invalid values"): Likewise.