file re-organization
blank line at the end
generic functions for size and eltype
throw a DimensionMismatch instead of raising an error
blank line before EOF
refactor the testing paradigm
introduce pdadd & pdadd! in the place of add and add_scal
refactor arithmetics
refactored transformation
remove some util functions
remove unwhiten_winv!
add tests for whiten! and unwhiten!
refactored whiten & unwhiten
refactored quad and invquad
refactor tri products
relax types
refined PDMat constructor API
allow uplo for PDMat construction
update read
update readme