Insert reference has extraneous brace and lowercases title

[jschwab]

This uses the same bibtex entry as in #163.

At present, the Insert Reference action produces

- Paxton}, B., Marchant, P., Schwab, J., Bauer, E.~B., Bildsten, L.,
  Cantiello, M., Dessart, L., … (2015). Modules for experiments in
  stellar astrophysics (mesa): binaries, pulsations, and
  explosions. \apjs, 220(),
  15. http://dx.doi.org/10.1088/0067-0049/220/1/15

There is an extraneous brace after the 1st author (Paxton) and the title has been inappropriately lowercased.

Running git bisect gives first bad commit: [b2f5430]

[jschwab]

Both of these problems may be due to an over-aggressive stripping of curly braces in bibtex-completion-get-value. If I modify that function not to strip curly braces, then both the author and title look as expected.