Flux 1.4.0 release

This release includes a rewrite of the YAML updating code, removing the restrictions on using List resources and files with multiple YAML documents, as well as fixing various bugs (like being confused by the indentation of container blocks).

See https://github.com/weaveworks/flux/blob/1.4.0/site/requirements.md for remaining constraints.

The YAML parser preserves comments and literal quoting, but may reindent blocks the first time it changes a file.

Fixes

• Correct an issue the led to Flux incorrectly reporting resources as read-only weaveworks/flux#1119
• Some YAML update problems were fixed by the rewrite, the most egregious being:
  • botched releases when a YAML has indented container blocks
    weaveworks/flux#1082
  • mangled annotations when using multidoc YAML files
    weaveworks/flux#1044

Improvements

• Rewrite the YAML update code to use a round-tripping parser, rather than regular expressions
  weaveworks/flux#976. This removes the restrictions on how YAMLs are formatted, though there are still going to be corner cases in the parser (verifying changes will mitigate those by failing updates that would corrupt files).