Bump version to 0.7.0

minor fix

bump version to 0.6.1

removed dependency on collection

add StaggeredTile.fit constructor

bump version to 0.5.0

Make the childCount parameter of SliverMasonryGrid constructors, null…

…able and not required

fixed position issue with staired pattern

bump version 0.5.0-dev.6

bump to 0.5.0-dev.5