LTO is broken on some systems and should be used carefully. Thus this
option is removed from configure and LTO can be enabled by custom CFLAGS.

close #458

Set TC flag for incomplete glue

close #459

See merge request !534

For mandatory signature, we could stop processing the packet if the
buffer is too small. The response will have the TC flag anyway.

For optional signature, we can stop the processing as well. Because the
optional records are inserted into the additional section at last.

closes #197

refs #459

refs #459

Document supported PKCS 11 devices



See merge request !531

unit tests for heap



See merge request !533

Avoid gethostname() call in tests. It may cause long execution time in
case the network name resolution is slow.