Version 2.7.3

• Allow error summary to take a presenter argument for further customisation of the error summary list. The default presenter implements the current behaviour (it displays the first error for each attribute) but gives developers full control over the output. There's a new section in the guide covering its use. Many thanks to @jsugarman for this #311
• Refactor some of the label/legend content building, move from #compact#first to #find(&:presence) #308