v0.5.0 Release

[ Guillem Jover ]

• Update default upstream gitignore directories.
  Add _build as that's the default build directory. Anchor both _build
  and .pc under the root source by prefixing with «/». Mark them as
  directories by suffixing with «/».
• Place license location on the filesystem in a Comment field.
  This is not part of the license statement, it's rather an ancillary
  comment about where to find it.

[ Peymaneh Nejad ]

• Add step (go.step.sm) to knownHosts

[ Federico Grau ]

• Check for and move upstream debian dir if it exists (Closes: #983241)

[ Arnaud Rebillout ]

• Make sure to call normalizeDebianProgramName() on the whole name,
  not on parts.
• Renaming: normalizeDebian{Program,Package}Name
• Add testcases to nameFromGoPkg: golang.org/x/term and two others.
• Update debian-policy link url
• Set debianBranch in execMake(), use it in createGitRepository()
  This minor refactoring prepares the code for the next commit, where we
  will need to know the Debian branch in execMake().
• Fix make output: run 'git push' before 'gbp push'
  As mentioned in #107, running 'gbp push' when there's no debian tag is
  not the right thing to do, as it will only push the upstream branch.
  Consequences are:
  1. The default gitlab branch is set to the upstream branch instead of
     the debian branch.
  2. The debian branch is not pushed and needs to be pushed manually
     anyway.
     I believe that the best thing to do instead is just to run 'git push
     origin ' first, and then run 'gbp push'.
• Keep compatibility with Git below 2.28.
  Thanks to Alois Micard for pointing that out

[ Aleksey Morarash ]

• Extend .gitignore with vim temporary files
• Annotate errors with context.
  This will prevent situations when program terminates with bare error
  leaving the user without any clue of where the error was occurred.

[ Anthony Fok ]

• Set GO111MODULE=off when calling go list etc.
  to keep dh-make-golang make and estimate working with Go 1.16 and 1.17
• Add "Multi-Arch: foreign" to library packages in debian/control
• Add Expat (MIT) license text template
• Update Standards-Version to 4.6.0
• Recognize upstream pre-release versions so that tilde ~ instead of -
  is used in upstream tarball and in debian/changelog, e.g. 1.0.0~rc1 instead of 1.0.0-rc.1.
  Thanks to nicoo (Closes: #981421)
• Workaround go list error when upstream uses ../.. in import path
  (Closes: #992610)
• make: Add -program_package_name flag.
  This allows overriding the program package name, and the source package
  name too when appropriate, e.g. to name github.com/cli/cli as gh.
  See discussion at #951374
• make: Change -force_prerelease and -upstream_git_history flags
  to use underscore instead of hyphen
• make: Change some wordings in help and instruction, especially
  the use of git commit -S for signing the commit
• Add fyne.io as "fyne" to knownHosts
• Add filippo.io as "filippo" to knownHosts
• Fix SA1006 and ST1005 reported by staticcheck
  • ST1005 Incorrectly formatted error string
  • SA1006 Printf with dynamic first argument and no further arguments
• Migrate from Travis CI to GitHub Actions workflow for CI tests
• Bump dependencies: Go >= 1.13 and github.com/google/go-github to v38