For #45: Fix popping up/down window for search with single match

- New with-display-buffer-no-window and use it.

- Improve calculation of ggtags-global-output-lines and use it to
  avoid (line-number-at-pos (point-max)) all the time.

- Make ggtags-global-handle-exit display buffer for multiple matches.
New function ggtags-echo and use it
Fix #45: Change default value of ggtags-auto-jump-to-match

Fix ggtags-global-filter not to show the point-max of *ggtags-global*
buffer or users will see the scrolling text.

Do not auto jump to history if users have manually jumped to an error
i.e. compilation-current-error is non-nil.
Add NEWS to README.rst for 0.8.0 and 0.8.1
New function ggtags-eldoc-function for eldoc support

Refactor ggtags-show-definition for re-use by replacing
ggtags-show-definition-function with ggtags-get-definition-function
and ggtags-print-definition-function.
Fix error in approximation to (line-number-at-pos (point-max))

ggtags-global-output-lines >= (line-number-at-pos (point-max)) is not
always true.
Refactor out ggtags-include-file from ggtags-find-tag-dwim

Do not move point to the beginning of line if ggtags-include-pattern
is a function otherwise it cannot access the value of point.
Don't activate eldoc support by default

since it is difficult to enable it without overriding users' settings
for emacs <= 24.3.