Define new `haskell-mode-pkg-base-dir` defvar

Because `haskell-mode-pkg-base-dir` is also used for initializating
`haskell-process-logo` now this fixes #102 as a side-effect.
New `M-x haskell-mode-view-news` command for viewing NEWS file
Convert NEWS to outline/org mode format and add placeholder entries

This also adds NEWS to PKG_DIST_FILES

The empty placeholder NEWS entries will be supplied shortly. The new
format is optimized for use in combination with
`M-x haskell-mode-view-news` committed earlier via bc615ca.
Add hint about `M-x haskell-mode-view-news` in long package description
Write belated NEWS entry for version 2.9.x
Write missing NEWS entry for version 13.6
Add preliminary NEWS entry for yet to be released ver 13.7
Fix typo in NEWS file introduced in 0a97d9e