Automatically generate ChangeLog from git logs

The ChangeLog file is now automatically generated from git commit logs.
The target range of commit logs is specified using GIT_START_POINT in
Makefile.am, as the older boundary, up to HEAD. GIT_START_POINT can be
a date, a git tag, a git hash, ... See gitrevisions for more information
on specifying ranges

This work is inherited from the one of Charles Lepple, on the project
NUT - Network UPS Tools <http://networkupstools.org>
Add ChangeLog to the git ignored files
Disable distcleancheck due to the dist generated files

The automated generation of the ChangeLog file introduced an issue in
the distribution chain, leading to ChangeLog being left at distclean
time, while it should have been removed. The distcleancheck_listfiles
workaround (commented) works fine on modern systems, but may cause
issues on older unix systems. This commit disables distcleancheck, and
leaves to CZMQ maintainers the choice to enable distcleancheck_listfiles
or not
Merge pull request #736 from aquette/autogen-ChangeLog

Automatically generate ChangeLog from git logs