Add multiple source file and templating support to file.append (#6905)

Allow states/file.append() to use multiple source files and templating
to generate the text to be appended to the 'named' file.
Update Docstring
Remove the warning about bug #7290 now its fixed.
Added template context on rendering error

When a template rendering error occurs, show the part of the template
where the problem happened in order to make it easier to track down.
Added tests for error template context.
`0.17.0` has been tagged. The `0.16.x` `requires_network` is no longer necessary.
Fixed type-o
Merge pull request #7344 from holmboe/develop

Upcase constant
Merge pull request #7345 from evinrude/develop

Spelling fix
Merge pull request #7342 from s0undt3ch/hotfix/requires-network

`0.17.0` has been tagged. The `0.16.x` `requires_network` is no longer necessary
fix #7339
Merge pull request #7346 from pille/patch-2

fixes #7339
Adding versionadd's for salt cli ref and salt.states.file to denote some new 0.17 features
Merge pull request #7348 from JustinCarmony/doc-version-fixes

Adding versionadd's for salt cli ref and salt.states.file
Properly handle `git describe` with RC's and proper version comparison.
Properly handle shell unit tests which check versions.
fix missing man page for salt-ssh fixes #7042
Render errors are critical
Merge pull request #7355 from aboe76/salt-ssh-manpage

fix missing man page for salt-ssh fixes #7042
Merge pull request #7358 from jesusaurus/render/error

Render errors are critical