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"
Simplify "Getting updates with git pull"
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
glossary: remove outdated/misleading/irrelevant entries

Signed-off-by: Thomas Ackermann <th.acker@arcor.de>
glossary: improve description of SHA-1 related topics

The name of the hash function is "SHA-1", not "SHA1".

Also to people who look up "object name" in the glossary,
the details of which hash function is applied on what to
compute "object name" is not important but the fact that the
name is meant to be an unique identifier for the contents
stored in the object is.

Signed-off-by: Thomas Ackermann <th.acker@arcor.de>