Fix contribution requirements for provisioning

Thanks, @Wilfred

[ci skip]
[Fix #497] Handle empty messages from Clang
Fix style

[ci skip]
Bump Cask version
Fix Javascript test cases
Install js-yaml first
[Fix #398] Make minimum error level for navigation customizable
Allow nil value for error level
Change default to nil
Document the new option
Improve helper macro for navigation tests
[Fix #485] Merge branch 'minimum-error-level'

* minimum-error-level:
  Improve helper macro for navigation tests
  Document the new option
  Change default to nil
  Allow nil value for error level
  [Fix #398] Make minimum error level for navigation customizable
Update credits, changelog and texinfo manual [#485]
[Fix #490] Remove error list highlighting for errors at point

Highlighting errors at the current line should be totally sufficient,
and not highlighting errors at point separately makes the highlighting
more predictable.
Inline internal error list functions
Add separate error list column for syntax checker type

Makes the appearance of the syntax checker type customizable
[Fix #500] Merge branch 'colorized-checker-type'

* colorized-checker-type:
  Add separate error list column for syntax checker type
  Inline internal error list functions
Update credits and changelog [#500]
Document error list faces [#500]
Slightly refine credits