Updated public API to version 2.1.

The document title was not set to version 2.1.  The new version was also used to
update the online documentation.  Furthermore, the makefile was fixed to use a
bash shell to fix the echo -e problem.
Unified handling of CC term creation.

There was a function specifying the need for a CC term and the CCTermBuilder had
the same code inlined.  This code was unified to simplify maintenance.
Ommit doomed tests.

The delta debugger still tested the whole right part after splitting a failure
block into a left and a right part and receiving a success on the left part.
The test on the right part cannot succeed.  Now, it will be skipped and the
right block (called a buddy) will be split on success of the left block.
Removed print debugging output.

A print debugging line was left over in NeutralRemover.  Since it is unneeded,
it was removed (not turned into a debug message).
Bugfixes and performance improvments.

The delta debugger did not correctly detect and remove neutral elements.
Sometimes this led to testing the current term due to errors in the removal
process.  This caused non-termination since the remove neutrals phase was always
considered successful.  I added an assertion to detect this problem.

During the whole delta debugging time, only two output reapers are used.  The
are reinitizialized on every test to reap the output of the new process streams.
Fixed unsoundness bug in LIRA logic

Freedom intervals did not respect infinitesimal parts.  This led to an
unsoundness bug in the LIRA case where an integer was found in the freedom
interval that was not really there.
Prevent models for unknown result

SMTInterpol crashed when the solver timed out but the user wanted to create a
model.  This happens, e.g., when the solver did not get to ensureIntegrals() and
thus tries to create a non-integral value for an integer variable.  This update
now tells the user that models are not available if the solver returned unknown.