v0.5.0: i understood that reference

new features

• ambiguous references (those which can be satisfied by multiple tags) now
  result in an error, just like broken references (those matching no tags). to
  suppress the error, pass --allow-broken-references, as with broken
  references.

• broken and ambiguous references will result in a warning during compilation;
  this makes it easier to hunt them down and fix them while using
  --allow-broken-references.

• sped up build time when building with plugins, by using go install instead
  of go build