VERSION bump version to 0.4.20
VERSION bump version to 0.4.20

cherry-pick some bugfixes from 0.5 branch

PavolVican/libyang,PavolVican/libyang,PavolVican/libyang,lukasmacko/libyang,PavolVican/libyang,PavolVican/libyang,lukasmacko/libyang