Replace `libguile-ssh' with `Guile-SSH' in commentaries.

* Makefile.am, am/Makefile.am, ssh/Makefile.am, ssh/auth.c,
  ssh/auth.h, ssh/auth.scm, ssh/base64.c, ssh/base64.h,
  ssh/channel-func.c, ssh/channel-func.h, ssh/channel-main.c,
  ssh/channel-type.c, ssh/channel-type.h, ssh/channel.scm,
  ssh/common.c, ssh/common.h, ssh/error.c, ssh/error.h,
  ssh/key-func.c, ssh/key-func.h, ssh/key-main.c, ssh/key-type.c,
  ssh/key-type.h, ssh/key.scm, ssh/message-func.c,
  ssh/message-func.h, ssh/message-main.c, ssh/message-type.c,
  ssh/message-type.h, ssh/message.scm, ssh/server-func.c,
  ssh/server-func.h, ssh/server-main.c, ssh/server-type.c,
  ssh/server-type.h, ssh/server.scm, ssh/session-func.c,
  ssh/session-func.h, ssh/session-main.c, ssh/session-type.c,
  ssh/session-type.h, ssh/session.scm, ssh/threads.c, ssh/threads.h,
  ssh/version.c, ssh/version.scm, tests/Makefile.am,
  tests/client-server.scm, tests/server-client.scm,
  tests/server.scm, tests/session.scm, tests/sssh-ssshd.scm,
  configure.ac: Replace `libguile-ssh' with `Guile-SSH' in
  commentaries.
NEWS: Bump version to 0.6.0

* NEWS: Bump version to 0.6.0
* doc/version.texi: Likewise.
* configure.ac: Likewise.  Change URL of the project.