add Transpose
add LDLT
make LDLT a Policy, and write Decomposition host class for it
remove node_type from traits

currently unused
add LogDeterminant, only specialized on LDLT
make LogDeterminant general, no specialization

will only work with LDLT though
Revert "make LDLT a Policy, and write Decomposition host class for it"

This reverts commit f26fec44118a59f6464981081f9bf59fa7503d2b.

Conflicts:
	include/internal/Decomposition.h
	include/internal/ForwardDeclarations.h
	include/internal/LDLTPolicy.h
	include/internal/MatrixBase.h
	test/test_GPMatrix.cpp
rename LDLT in Decomposition
export LDLT as policy from Decomposition
decouple LDLT from Decomposition

Decomposition now accepts a generic Policy type
rewrite determinant to be a specialization for LDLTPolicy