NEWS: Add the descriptions for 0.5.0 release

[dongahn]

Took liberty of posting this PR so that we can continue to edit if needed.

Drafted by @grondo and minor edits by @dongahn.

[grondo]

Sounds good to me! I'll merge asap and then want me to push a 0.5.0 tag?

[dongahn]

I'll merge asap and then want me to push a 0.5.0 tag?

[dongahn]

I'll merge asap and then want me to push a 0.5.0 tag?

Yes, please!

[codecov-io]

Codecov Report

Merging #342 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #342   +/-   ##
=======================================
  Coverage   73.34%   73.34%           
=======================================
  Files          59       59           
  Lines        9840     9840           
=======================================
  Hits         7217     7217           
  Misses       2623     2623

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[coveralls]

Coverage remained the same at 74.8% when pulling c08256a on dongahn:news into 69767b4 on flux-framework:master.

[grondo]

Ok, v0.5.0 is tagged and a release tarball should pop out of Travis momentarily.

I'll build packages for TOSS 3 on Monday.