Fixed usage of json-c lib >= 0.10.

json-c changed the handling of 64 bit wide integers and got rid of
json_type_int64 which we used. This broke compilation on systems
with current json-c libraries.
Updated pkg-json.c to work with all released versions (I hope.)
Merge pull request #4 from zesstra/json64-fix

Fixed usage of json-c lib >= 0.10.
Changed the homepage URL.
Removed copyright note about PCRE.

We don't ship a bundled version of the PCRE package anymore
(but link against it the one installed on the host system).
So the note is superfluous.
Added new contributors in CREDITS.

New section for contributions in the time since Lars Duening
(if we missed someone, please contact us - sorry).
Moved CREDIT for XML support from COPYRIGHT to CREDITS.
Renamed CHANGELOG to CHANGELOG.OLD.

We don't maintain the CHANGELOG since 2011.
New CHANGELOG file.

It contains a hint to the git log command, the HISTORY and
CHANGELOG.OLD for changes until june 2011.
Updates to the INSTALL document.

updated note about: IPv6, 64 bit systems, 32 bit binaries on 64 bit
systems, compiling from our source repository, optional libraries,
compiling for Windows.