Add new methods for supporting data frame use to NEWS

NEWS.md

@@ -1,5 +1,10 @@
 # autodb (development version)
 
+## Improvements
+
+* Added `format` and `as.data.frame` methods for `functional_dependency`, `relation_schema`, `database_schema`, `relation`, and `database`. This allows them to be columns in a data frame at initial construction. I'm not sure *why* you'd want to put them a a data frame column, but it's consistent with the idea that the objects from these classes should mostly be treatable as vectors. Be warned: they don't currently work in tibbles.
+* Added an `as.character` method for `functional_dependency`. The optional `align_arrows` argument can add padding to one side, in order to make the arrows align when they're printed to different lines. These options are used to align arrows in its `print` method, and its `format` method for when printed as a data frame column.
+
 ## Fixes
 
 * Fixed `gv` to account for Graphviz HTML-like labels requiring certain characters, namely the set "<>&, to be escaped in Graphviz HTML-like labels, and removed completely in attribute values.