Updating php-font-lib
minor test updates
Update CONTRIBUTING.md
Account for \n at start of xref in startxref

Although (most) PDF readers seem to cope with an incorrect startxref value
it is off by one and can cause problems with other PDF libraries if they
trust the startxref value (i.e. they don't account for this issue).
Update php-font-lib requirement
Revert "Update php-font-lib requirement"

This reverts commit ffb51908cb6036a096b25c96a3f65dd30144f893.
Little bit of cleaning up for 0.6.0 final