add: modular.lib
(cherry picked from commit 4033c6b71b5bdc43798b4183c90512f5d4871308)

Signed-off-by: Andreas Steenpass <steenpass@mathematik.uni-kl.de>

Conflicts:
	Singular/singular-libs
Merge pull request #555 from steenpass/modular_sw

add: modular.lib
Merge pull request #550 from adipopescu/Spectrum

Separation of SPECTRUM-related code inside `kernel/`
add: Tst/Short/modular_s.tst to ok_s.lst
Separating Sources kernel/linear_algebra
Separating Headers: kernel/linear_algebra