Call it "Git User Manual" and remove reference to very old Git version
Remove "Notes and todo" section
Move glossary to end of user-manual
Improve formatting for user-manual html and pdf output

- Change asciidoc title level.
  This removes blank first page and "Part I" page
  (there is no "Part II"!) in pdf output
- Use style 'article' instead of 'book'.
  This removes sub-tocs and chapter numbering in html output
Fix typos and suboptimal wording
Improve clarifications and consistency in "Manipulating branches"
Use current "detached HEAD" message
Simplify "How to make a commit"
Improve description in "How to merge"
Remove obscure reference from "Examples"
Use "git merge" instead of "git pull ."
Use current output for "git repack"
"git prune" is safe nowadays; isn't it?
Remove irrelevant reference
Fix description in "Merge multiple trees"; remove unnecessary quoting
Remove unnecessary historical note
XXX Disable reconfiguration; create and ignore .mobi