make y, w and w_hat r/w properties
force use of precomputation flags
fix missing colons
restore PRECOMPUTE_* flags
fix #20: expose solver internals as RO properties
Merge branch 'develop' into bug/solver-fix-props
add cdef'd attributes declaration in Solver class
initialization done on ravel'd arrays
fix #25: add missing import_array, no more segfaults
Merge branch 'bug/solver-fix-props' into develop