Doc fix: Update README.rst and doc-strings
Rename try-complete-ggtags-tag to ggtags-try-complete-tag

Update README.rst.
Enhance ggtags-view-tag-history to use next-/previous-error

- New major mode ggtags-view-tag-history-mode derived from
  tabulated-list-mode with custom key bindings.
- Update README.rst.
Fix #12: Remove ggtags-completing-read-function

Not needed and may get in the way.
Fix typos.
Change ggtags-read-tag to completing-read when no default

Shell-quote NAME to ggtags-find-tag-dwim, ggtags-find-reference and
ggtags-find-other-symbol.
Fix ggtags-try-complete-tag to use ggtags-bounds-of-tag-function
Fix #42: Clear ggtags-project-root in non-file buffers