doc new `app` stanza and update tests to use it

Replacing `link` for almost all cases.

The `link` stanza can still appear in error messages, because
under the hood, `app` is still implemented as a pure synonym
for the `link` artifact.  That will change automatically when
we factor into separate artifacts.
Add VoodooPad 5.1.3
Merge pull request #6171 from kejadlen/voodoopad

Add VoodooPad 5.1.3
Add Hunt X.app v0.1

Product Hunt for Mac. The Startup List for awesome people!
Merge pull request #6186 from vinkla/hunt-x

Add Hunt X.app v0.1
Refactor {develop,production}_brew_cask

Almost all of these two scripts are identical. Refactor out the common
bits, saving over 60 lines of repetition.

Right now this is handled by moving all the logic into "develop_brew_cask"
and symlinking "production_brew_cask".

This will be followed by another patch to add a "manage_brew_cask_links"
command to do the same with sub-commands, e.g.,
  manage_brew_cask_links status
returns "production" or "develop",
  manage_brew_cask_links production
does the same as production_brew_cask,
  manage_brew_cask_links develop
does the same as develop_brew_cask, etc. At that point, I'd like to
rename the script "manage_brew_cask_links" and have the two present
names be symlinked to that.

This was motivated by (besides DRY) getting tired of having to
manually check symlinks to see which state I was currently in.
Upgrade Inastacast to v1.2.6

Instacast version 1.2.6 is available for download from vemedio with sha256
560922bd0ccc7ebab002035d80ae4e630d6f30fde7eebacb7dff616e633a1a4d.
Upgraded the formula to install this version.
Merge pull request #6188 from asmod3us/instacast-126

Upgrade Instacast to v1.2.6
Merge pull request #6187 from treyharris/refactor-develop_brew_cask

Refactor {develop,production}_brew_cask
Bump jaspersoft to 5.6.1.
Merge pull request #6191 from ctwise/jaspersoft-5.6.1

Bump jaspersoft to 5.6.1.
Merge pull request #6167 from rolandwalker/doc_app_stanza

doc new `app` stanza and update tests to use it