LDAP.pm: prefer IO::Socket::IP over IO::Socket::INET6

Check whether IO::Socket::IP 0.20 or higher exists, and if it does
use it to create IPv6 & IPv4 sockets.
Otherwise, check for IO::Socket::INET6 and use it when it is available
for both, IPv4 & IPv6 socketr
In all other cases, support IPv4 only using IO::socket::INET.
LDAP.pod: remove wrong note about IO::Socket::IP

In a mail conversation with Paul Evans, the author of IO::Socket::IP,
I learned that IO::Socket::IP does indeed support the Timeout option.

Hence, this note, added in commit d547b965d0f7830eaedf06b272fac98e7b467846,
is wrong and needs to be removed.
README: mention IO::Socket::IP
t/40connect.t: adapt to check for IO::Socket::IP too
FAQ.pod: mention IO::Socket::IP
Filter.pm: fix bogus references in comments
contrib/*: space police - remove trailing spaces
META.json: "suggest" IO::Socket::IP
Merge pull request #30 from marschap/next

prepare next release
Release 0.60