Prepare for v1.4.0 release

[lognaturel]

Release with background audio recording support in preparation for ODK Collect release.

• [x] Make sure the version of ODK Validate in the repo is up-to-date
• [x] Run all tests through Validate
  • I fixed a few tests that were easy to address; there are a few that still fail but no new ones
• [x] Draft a new GitHub release with the list of merged PRs.
• [x] Checkout a release branch from latest upstream master.
• [x] Update CHANGES.txt with the text of the draft release.
• [x] Update README.rst, setup.py, pyxform/init.py with the new release version number.

[codecov-io]

Codecov Report

Merging #520 (1abc8e5) into master (6886234) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #520   +/-   ##
=======================================
  Coverage   83.92%   83.92%           
=======================================
  Files          25       25           
  Lines        3713     3713           
  Branches      865      865           
=======================================
  Hits         3116     3116           
  Misses        452      452           
  Partials      145      145           

Impacted Files	Coverage Δ
pyxform/__init__.py	100.00% <100.00%> (ø)

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[yanokwa]

@lognaturel Can you please file an issue with the tests that fail, or comment them out? It's fine that we are ignoring them, but we should document it.