Caliper v1.6.0

Analysis-engine release: a caller can now see which packages the load dropped and which loaded packages the call graph leaves out, and why.

Added

• Engine.Failed() returns the packages the load dropped (#38).
  Packages() leaves out every package with errors, and until now
  nothing recorded that they existed, so a caller describing the whole
  module could not tell a package that failed from one that does not
  exist. Failed() returns them with their Errors and whatever
  go/packages kept: the syntax that parsed, and for a partly
  type-checked package, the Types scope and TypesInfo of the
  declarations that resolved. A directory whose files a build
  constraint all excludes is still absent, because ./... does not
  match it.

• InterProceduralContext.Skipped lists the loaded packages left out of
  the SSA program, each with the Cause: the package whose error outside
  a function body put it out of reach. Such a package is in Packages()
  and type-checked cleanly, but imports, possibly transitively, a package
  with a declaration or syntax error, so it has no functions and no
  call-graph edges. Before, that was silent.