dist: substitute ```@VERSION@``` and ```@DATE@``` tokens

During "make dist", iterate through README and all the man pages
substituting ```@VERSION@``` with the current version number and
```@DATE@``` with today's date (in the form YYYY-MM-DD).

Signed-off-by: Jeff Squyres <jsquyres@cisco.com>
README: Add ```@VERSION@``` and ```@DATE@``` tokens.

Signed-off-by: Jeff Squyres <jsquyres@cisco.com>
man: add ```@VERSION@``` and ```@DATE@``` tokens to all man pages

Signed-off-by: Jeff Squyres <jsquyres@cisco.com>
Merge pull request #236 from jsquyres/pr/dist-man-pages

Have "make dist" seed the README and man pages with today's date and the version