Replace an expensive expand_one call with the cheaper unescape_string

Makes parsing a little faster
Fix to avoid generating multiple error nodes on parse error
Tweak comment handling. Mark a parse node with a new flag when it has comments
Clean up the last token when receiving TOK_END
Include fallback.h in output.h to avoid a compile error
Allow running specific high-level tests by passing the name to test.fish

Example:
  tests/test.fish expansion
This will run the tests in expansion.in only
Rewrite of fish_indent

Changes fish_indent to leverage new parse tree
Also supports colorizing output via --html and --ansi flags.
Implement tests for fish_indent
Correct path in fish_indent tests
Update fish_indent Xcode build target
Improve indentation of blocks inside if/while headers

Fixes #1665
Document new flags to fish_indent
Tmuxinator completions
Fix for assertion failure in fish_indent when setting a non-RGB color
Clarify some documentation regarding fish_indent
Update completions for fish_indent
Use <pre><code> for fish_indent HTML output

As suggested in #1827
Close <code> before <pre> in fish_indent
test: note that the square bracket form is available

As requested in https://github.com/fish-shell/fish-shell/issues/1850