Update grid comments and example HTML

Make it clear that utilities or other components are to be used to
control the width of individual cells.

Include the latest sizing utility names in the example use.
Remove the default gutters from the grid

Since this is low-level it should have no default grid gutters.
Update 'suit-utils-dimension' to v0.2.0

Update the development dependency on 'suit-utils-dimension' to the
latest iteration of the package.
Update test file

Use new utility dimension names. Tweak style of test now that there are
no gutters.
Update CHANGELOG
Improve documentation

Add examples to the README and clarify the purpose of the component.
v0.3.0