Fix regression regarding $eval

In order to be useful $eval needs to evaluate the given string twice,
for example: `${eval $${downspeedf ${gw_iface}}}` should first yield
e.g. '${downspeedf eth0}', then the second evaluation yields the desired
result.
Commit 2fa5f97edbc2c77833bdef3ba0ac5663d5eb25d6 refactored some parsing bits
into the evaluate function, but this caused $eval to call
parse_conky_vars only once.
Remove unnecessary strncpy for $eval
Change PACKAGE to conky-ng

The rest is intentionally kept as conky for compatibility reasons.
Differentiate between conky and -ng in AUTHORS
Add cat.h to mandatory_sources in src/Makefile.am
Move NEWS to ChangeLog

Having a ChangeLog with no info besides changes for a given date is
rather useless. Next to that NEWS contains a ChangeLog per version,
which actually is somewhat useful.
Set foreign for AM_INIT_AUTOMAKE

Silly automake assumes this is a GNU project otherwise and that will
make it go mad at missing NEWS.
Update ChangeLog for 1.9.1