Warn about split-button dropdowns
Merge pull request #55 from zacechola/btn_dropdown_after_btn

Warn about split-button dropdowns
Check for input-group-* sizing

This checks that .input-group-* sizes are used on .input-group when
.btn-lg, .btn-sm, .input-lg and .input-sm are used within the
.input-group class.

Refs #47
Closes #54 by merging it (after squashing & trivial grammar fix)