GitLab

 - address_family_, default ctor removed from two parsers
 - copyright year updated
 - Element::getNonConst is now documented
 - user's guide is now clear about csv-format default value is now true

 It now contains vector of ElementPtr, rather than ConstElementPtr

Also, removed multiple references to DHCP4_CONFIG_LOAD_FAIL from the
DHCPv4 server and DHCP6_CONFIG_LOAD_FAIL from the DHCPv6 server.

Files reverted:

data::merge function is intended to merge to map elements together.
However, if those maps contain elements which are themselves maps they
are not merged.  The function uses recursion to merge map sub-elements.

this has been a bug, but it's now critical as libc++ makes it errors
for ifstream.

It has been asserted that using empty() is more efficient than using
size() > 0 due to the possible extra work size() has to do. So provide
an empty() function, which matches the underlying Boost implementation.

       Element::create accepts char, short, int, long, long long, int32_t and int64_t.
       IntElement->intValue() returns int64_t.
       IntElement->getValue() and IntElement->setValue() accept int64_t only.

       Now support LONG_MAX, LONG_MIN and floating underflow detection