Use named fields in *Martini initialization
Add a test that exposes a data race in (*Martini).createContext()

Run `go test -race` to reproduce. (*Martini).handlers is modified simultaneously by several goroutines.
Improve test to make sure it does not depend on append implementation details.
Fix data race by not appending to m.handlers but passing m.action instead to the context.
Merge branch 'vanackere-fix-handler-races'