don't test bitpackstring with array length 0

fixes issue #44
Merge pull request #45 from Garonenur/dw

don't test bitpackstring with array length 0
Merge pull request #46 from standage/master

Replacing GtResetSourceStream with GtSetSourceVisitor
change gt_ensure

gt_ensure now expects had_err AND err as valid variable in its scope.

closes #47
update devguide to reflect gt_ensure changes
Merge pull request #48 from Garonenur/ensure
coding style

unnecessary prefix was added by accident years ago
Merge pull request #50 from gordon/master

coding style
update documentation
fix piwik links

long story why this became necessary, but this is the simplest solution for now
Merge pull request #51 from gordon/master

website update