adding pack-<model>-src target

By calling pack-<model>-src the source files in the model directory
models/<model>/ will be packed into a tarball for separate
distribution.
explicitly disable Higgs two-loop corrections for the MRSSM
add MicrOMEGAS interface to the todo list
add S,T,U variables to the todo list
simplify implementation of AbsSqrt()
improve commet on @ModelName@_two_scale_model.cpp
do not hard-code the loop order in the debug output comments
calculate DR-bar MZ and MW at 1-loop order only if thresholds enabled

At the low-scale constraint MW and MZ (in the DR-bar scheme) are used
to calculate the Weinberg angle.  The Weinberg angle is used to
calculate g1 and g2.  I.e. MW and MZ are used to calculate threshold
corrections to g1 and g2.  Therefore, the calculation of DR-bar MW and
MZ from pole MW and MZ at the one-loop level should be done only if
threshold corrections are enabled.  If threshold corrections are
disabled, one should set MW(DR-bar) = MW(pole) and MZ(DR-bar) =
MZ(pole) .
remove annoying commertion at the begin of SLHA output
change threshold corrections on/off switch to loop order choice

The meaning and behavior of the values 0 and 1 is preserved.  Besides
these, higher values are allowed to enable higher loop corrections,
implemented later.
change threshold corrections on/off switch to loop order choice

continued
update Softsusy reference
Adapt custom betas example to commit d0e9cdba4e947f6a17a81f0dcd883aa572951f6d
Adapt custom betas example to commit cbe6df0c244f92bb54b08061578bcad4758740dd
avoid calling method twice
add SLHA class documentation
rename variable in SLHA writing methods
hide function which is not needed in other parts of the code

This fixes a shdw warning with SARAH 4.3.
add newline to improve readablility
avoid unnecessary declarations if ENABLE_THREADS is undefined

This reduces code size and compilation speed a bit.